Hi Jean-Ghislain,
Thank you very much for the details, it helps us a lot!
On the front-end error console there are a few messages about missing files from the wp-content/cache/ folder. I suspect that the file may actually exist, but there is either an incorrec .htaccess rule or a mod_rewrite condition, which redirects the request to the 404 page. This causes the problem with the plugin too, because the files are enqueued from that cache.
I would recommend checking if the wp-content/cache/ folder exists (the plugin reports that it does) and if there are any files within that folder. Then checking if there is no permission restriction applied. I suspect this is an issue with a mod_rewrite rule in the .htaccess folder, as the cache folder permission issues would likely been detected.
For now, I have resolved this by changing the compatibility settings like so: https://i.imgur.com/6ujtvR3.png
I still recommend investigating that cache folder and the .htaccess to see why it’s redirecting.
I hope this helps!