It worked. Thank you very much for your help.
The upgrade went well, except, I still receive the same warnings stated earlier, such as:
[18-Jun-2020 06:33:07 UTC] WARNING: Unable to find a match for “146-392-1-RV.docx” in “/home/journal1/private/files/journals/1//articles/146/”. Skipping this file.
[18-Jun-2020 06:33:07 UTC] WARNING: Unable to find a match for “154-460-1-RV.docx” in “/home/journal1/private/files/journals/1//articles/154/”. Skipping this file.
Besides, I received the following warnings/errors:
[20-Jun-2020 17:43:44 UTC] WARNING: Unable to find a match for “304-821-1-SM.pdf” in “/home/journal1/private/files/journals/1//articles/304/”. Skipping this file.
[20-Jun-2020 17:43:44 UTC] WARNING: Unable to find a match for "306-823-1-SM.pdf" in "/home/journal1/private/files/journals/1//articles/306/". Skipping this file.
[20-Jun-2020 17:43:44 UTC] WARNING: Unable to find a match for "306-826-1-SP.pdf" in "/home/journal1/private/files/journals/1//articles/306/". Skipping this file.
[20-Jun-2020 17:43:44 UTC] PHP Warning: copy(/home/journal1/private/files/journals/1//articles/64/attachment/64-1-257-1-13-20180314.pdf): failed to open stream: No such file or directory in /home/journal1/public_html/lib/pkp/classes/file/FileManager.inc.php on line 181
[20-Jun-2020 17:43:44 UTC] PHP Warning: copy(/home/journal1/private/files/journals/1//articles/92/attachment/92-1-289-1-13-20180429.docx): failed to open stream: No such file or directory in /home/journal1/public_html/lib/pkp/classes/file/FileManager.inc.php on line 181
[20-Jun-2020 17:43:44 UTC] PHP Warning: copy(/home/journal1/private/files/journals/1//articles/94/attachment/94-1-294-1-13-20180430.docx): failed to open stream: No such file or directory in /home/journal1/public_html/lib/pkp/classes/file/FileManager.inc.php on line 181
[20-Jun-2020 17:43:44 UTC] PHP Warning: copy(/home/journal1/private/files/journals/1//articles/96/attachment/96-1-299-1-13-20180430.docx): failed to open stream: No such file or directory in /home/journal1/public_html/lib/pkp/classes/file/FileManager.inc.php on line 181
[20-Jun-2020 17:43:44 UTC] PHP Warning: copy(/home/journal1/private/files/journals/1//articles/187/attachment/187-1-544-1-13-20190613.pdf): failed to open stream: No such file or directory in /home/journal1/public_html/lib/pkp/classes/file/FileManager.inc.php on line 181
[20-Jun-2020 17:43:44 UTC] PHP Warning: copy(/home/journal1/private/files/journals/1//articles/226/attachment/226-1-600-1-13-20190620.pdf): failed to open stream: No such file or directory in /home/journal1/public_html/lib/pkp/classes/file/FileManager.inc.php on line 181
[20-Jun-2020 17:43:44 UTC] PHP Warning: copy(/home/journal1/private/files/journals/1//articles/256/attachment/256-1-746-1-13-20191126.pdf): failed to open stream: No such file or directory in /home/journal1/public_html/lib/pkp/classes/file/FileManager.inc.php on line 181
[20-Jun-2020 17:43:44 UTC] PHP Warning: copy(/home/journal1/private/files/journals/1//articles/280/attachment/280-1-791-1-13-20200607.docx): failed to open stream: No such file or directory in /home/journal1/public_html/lib/pkp/classes/file/FileManager.inc.php on line 181
[20-Jun-2020 17:43:44 UTC] PHP Warning: copy(/home/journal1/private/files/journals/1//articles/306/attachment/306-1-826-1-13-20200612.pdf): failed to open stream: No such file or directory in /home/journal1/public_html/lib/pkp/classes/file/FileManager.inc.php on line 181
[20-Jun-2020 17:43:45 UTC] PHP Warning: copy(/home/journal1/private/files/journals/1//articles/64/submission/proof/64-2-257-1-10-20180314.pdf): failed to open stream: No such file or directory in /home/journal1/public_html/lib/pkp/classes/file/FileManager.inc.php on line 181
[20-Jun-2020 17:43:45 UTC] WARNING: Unable to copy article_suppementary_files entry with file_id 257 to review stage! Skipping this file.
[20-Jun-2020 17:43:45 UTC] PHP Warning: copy(/home/journal1/private/files/journals/1//articles/92/submission/92-2-289-1-2-20180429.docx): failed to open stream: No such file or directory in /home/journal1/public_html/lib/pkp/classes/file/FileManager.inc.php on line 181
[20-Jun-2020 17:43:45 UTC] WARNING: Unable to copy article_suppementary_files entry with file_id 289 to review stage! Skipping this file.
[20-Jun-2020 17:43:45 UTC] PHP Warning: copy(/home/journal1/private/files/journals/1//articles/94/submission/94-2-294-1-2-20180430.docx): failed to open stream: No such file or directory in /home/journal1/public_html/lib/pkp/classes/file/FileManager.inc.php on line 181
[20-Jun-2020 17:43:45 UTC] WARNING: Unable to copy article_suppementary_files entry with file_id 294 to review stage! Skipping this file.
[20-Jun-2020 17:43:45 UTC] PHP Warning: copy(/home/journal1/private/files/journals/1//articles/96/submission/proof/96-2-299-1-10-20180430.docx): failed to open stream: No such file or directory in /home/journal1/public_html/lib/pkp/classes/file/FileManager.inc.php on line 181
[20-Jun-2020 17:43:45 UTC] WARNING: Unable to copy article_suppementary_files entry with file_id 299 to review stage! Skipping this file.
[20-Jun-2020 17:43:46 UTC] PHP Warning: rename(/home/journal1/private/files/journals/1//articles/53/submission/review/53-1-194-1-4-20171207.docx,/home/journal1/private/files/journals/1//articles/53/submission/review/attachment/53-1-194-1-5-20171207.docx): No such file or directory in /home/journal1/public_html/classes/install/Upgrade.inc.php on line 2021
[20-Jun-2020 17:43:46 UTC] ERROR: Unable to move "/home/journal1/private/files/journals/1//articles/53/submission/review/53-1-194-1-4-20171207.docx" to "/home/journal1/private/files/journals/1//articles/53/submission/review/attachment/53-1-194-1-5-20171207.docx".
[20-Jun-2020 17:43:46 UTC] PHP Warning: rename(/home/journal1/private/files/journals/1//articles/72/submission/review/72-1-376-2-4-20180622.pdf,/home/journal1/private/files/journals/1//articles/72/submission/review/attachment/72-1-376-2-5-20180622.pdf): No such file or directory in /home/journal1/public_html/classes/install/Upgrade.inc.php on line 2021
[20-Jun-2020 17:43:46 UTC] ERROR: Unable to move "/home/journal1/private/files/journals/1//articles/72/submission/review/72-1-376-2-4-20180622.pdf" to "/home/journal1/private/files/journals/1//articles/72/submission/review/attachment/72-1-376-2-5-20180622.pdf".
[20-Jun-2020 17:43:46 UTC] PHP Warning: rename(/home/journal1/private/files/journals/1//articles/72/submission/review/72-1-376-1-4-20180622.pdf,/home/journal1/private/files/journals/1//articles/72/submission/review/attachment/72-1-376-1-5-20180622.pdf): No such file or directory in /home/journal1/public_html/classes/install/Upgrade.inc.php on line 2021
[20-Jun-2020 17:43:46 UTC] ERROR: Unable to move "/home/journal1/private/files/journals/1//articles/72/submission/review/72-1-376-1-4-20180622.pdf" to "/home/journal1/private/files/journals/1//articles/72/submission/review/attachment/72-1-376-1-5-20180622.pdf".
[20-Jun-2020 17:43:46 UTC] PHP Warning: rename(/home/journal1/private/files/journals/1//articles/116/submission/review/116-1-377-1-4-20180706.docx,/home/journal1/private/files/journals/1//articles/116/submission/review/attachment/116-1-377-1-5-20180706.docx): No such file or directory in /home/journal1/public_html/classes/install/Upgrade.inc.php on line 2021
[20-Jun-2020 17:43:46 UTC] ERROR: Unable to move "/home/journal1/private/files/journals/1//articles/116/submission/review/116-1-377-1-4-20180706.docx" to "/home/journal1/private/files/journals/1//articles/116/submission/review/attachment/116-1-377-1-5-20180706.docx".
[20-Jun-2020 17:43:46 UTC] PHP Warning: rename(/home/journal1/private/files/journals/1//articles/247/submission/review/247-1-763-1-4-20191207.docx,/home/journal1/private/files/journals/1//articles/247/submission/review/attachment/247-1-763-1-5-20191207.docx): No such file or directory in /home/journal1/public_html/classes/install/Upgrade.inc.php on line 2021
[20-Jun-2020 17:43:46 UTC] ERROR: Unable to move` /home/journal1/private/files/journals/1//articles/247/submission/review/247-1-763-1-4-20191207.docx" to "/home/journal1/private/files/journals/1//articles/247/submission/review/attachment/247-1-763-1-5-20191207.docx".
[20-Jun-2020 17:43:46 UTC] PHP Warning: rename(/home/journal1/private/files/journals/1//articles/250/submission/review/250-1-713-1-4-20190822.doc,/home/journal1/private/files/journals/1//articles/250/submission/review/attachment/250-1-713-1-5-20190822.doc): No such file or directory in /home/journal1/public_html/classes/install/Upgrade.inc.php on line 2021
[20-Jun-2020 17:43:46 UTC] ERROR: Unable to move "/home/journal1/private/files/journals/1//articles/250/submission/review/250-1-713-1-4-20190822.doc" to "/home/journal1/private/files/journals/1//articles/250/submission/review/attachment/250-1-713-1-5-20190822.doc".
[20-Jun-2020 17:43:46 UTC] PHP Warning: rename(/home/journal1/private/files/journals/1//articles/249/submission/review/249-1-718-1-4-20190827.docx,/home/journal1/private/files/journals/1//articles/249/submission/review/attachment/249-1-718-1-5-20190827.docx): No such file or directory in /home/journal1/public_html/classes/install/Upgrade.inc.php on line 2021
[20-Jun-2020 17:43:46 UTC] ERROR: Unable to move "/home/journal1/private/files/journals/1//articles/249/submission/review/249-1-718-1-4-20190827.docx" to "/home/journal1/private/files/journals/1//articles/249/submission/review/attachment/249-1-718-1-5-20190827.docx".
I have searched for every single file, and they all exist in the corresponding exact folders (inside sub-folders such as submission, original, copyedit, etc).
I copied each group of files that belong to a specific article from sub-folders into the main folder of the article,… I got the same warnings.
I changed the permissions of all files and folders to 777 and repeated the upgrade (with a fresh database and OJS files), but to no avail.
What can I do to ensure that all these files can be migrated smoothly with the upgrade to 3.2?
Will it be OK to proceed with the current upgrade (with these warnings), run the OJS system, and re-attach every one of these files to their corresponding articles via the OJS system?
Thanks again for your help.