Hi,
I can confirm that this solves the problem. Thank you so much.
I still do not understand why the supplementary files get file_stage=2 during the upgrade. Hopefully this does not create other problems later on?
The same thing happened when I installed a fresh 2.4.8.1., created on journal, one issue and one article with one galley file and one supplementary file. The supplementary file had file_stage=2 after an upgrade to OJS3 and the galley view did not load.
ps. if possible, please comment my issue here: OJS 3.0 upgrade fails to move/rename some supplementary files I will do another test upgrade on Friday and it would be nice to solve the extension problem as well. As I said, I can of course run a script of my own pre-upgrade, but this is probably something that other users will experience as well.