I know you are now at JEM2 but just out curiosity: what was the problem you were running into with JEM3? Did test a version locally today with PHP 7.3.5 and it seems to be working. Did see there are some things to be changed, including the Zebra class.
Can it be that JEM 2 basically does not support subfolders in pictures?
Hmm, i would say yes that's the case but am not sure what's been changed in the latest versions of JEM2. That's something i might be able to look into tomorrow.
Did take a quick peak at JEM2 (v2.2.3) and am seeing that the image-handling is handled different then in JEM3 so using subfolders is not possible. When uploaded it's moved in a dedicated directory and there is no way to choose the directory.
Within JEM3 the media type formfield is being used and there is some code to create thumb-directory's etc.. In JEM2 images should be in the images/jem/event directory and the thumbs in the dedicated thumb directory. Besides that you've to check if all the data in the table (image-field) is pointed to that directory correctly.
Maybe i did understood you incorrectly but if so i do like to a screenshot to indicate the problem.
// btw, did also see a few little errors but think the team is working on that already.
If JEM2 isn't working out for you then i might help you out with addressing the problems you've with JEM3 + PHP7. Be aware that JEM2 is the path that's under active development. Jem 3 is not supported. This as there was decided some time ago to continue the JEM2 path and let JEM3 rest.
Aldo It's been a while back I can see what can be done. After your post I did install a version JEM3.0.7 locally and am modifying it to be up-to-date, or at least to get rid of the notes in the php error log. The thing is that i won't post the changes to the Github jemproject-JEM3 repo for now, this as JEM3 is not the "active development path".
Maybe i will post it to Github buth then in a personal repo so you can see what changes can be made.. But if you run into something i'd like to hear that too. Ah well you may PM me.