We’re seeing similar errors. We had some issues which were fixed in OJS 3.2.1.2, but now we’re seeing many lines like:
PHP Notice: Array to string conversion in /var/www/html/ojs/lib/pkp/classes/search/SubmissionSearchIndex.inc.php on line 37
and a few lines like:
I/O Error: Couldn't open file '/opt/ojs/files//journals/12//articles/6572/submission/proof/6572-121-9089-1-10-20200901.pdf': No such file or directory.
All those lines are proofs and the PDFs may have been deleted.
When upgrading to OJS 3.2.1.1, we saw keyword errors as described in [Upgrade 3.0.2.0 -> 3.2.1-1 keywords being lost in upgrade].