After doing some research, I still cannot understand why my assets in the bundles folder return 404 errors when I try to reach them.
I can see the files on the server, but when I try to reach them, symfony returns a 404 error.
For example, I have this file on the server : web/bundles/aluser/images/li-plus.png, but trying to access it with https://my-site.com/bundles/aluser/images/li-plus.png returns a 404 error. But on the other hand I can access files in https://my-site.com/images/li-plus.png for example.
I did the assets install and dump commands, cleared the cache but no results.
Thank you.
Thank you all for your answers,
they pointed me in the right direction (a problem with the server) : I did a asset install and dump commands with the root user of the server, all files created were then associated to this root user, and apache wouldn't serve them anymore.
After a chown, everything was working again. Thanks again :)