Hi Mel,
The issue was simply this option – actually not the option but the custom handler file was not longer accessible from the front-end, so I turned it off, now it’s okay: https://i.imgur.com/MRgnMqI.png
The file mask or the permissions must have changed, even installing the older versions the issue persists, as the file permission does not allow direct access on the newly copied files. That or there is a mod_rewrite or firewall ban on direct file access from plugin directories.