I have been using RC for couple years now, and I serve it under a subpath like https://DOMAIN/rc/ which has worked great all this time, no problems with uploads or chats.
I recently upgraded with docker pull. Now everything still works except that my uploads and the previews are broken. The reason it seems that they are served under file-upload instead of rc/file-uplaod
(based on the js console)
Preview Url
https://DOMAIN/file-upload/oAmmYnCNZcKdchBHp/test.jpg (this file naturally is broken in the client app)
There are a number of bugs on this as well - you should always check these things in the release notes and Issue before upgrading.
However, with the recent growth of Rocket.Chat there have been discussions about whether we should either drop support completely, or continue it. This has not yet been resolved so I have no definite answer here as yet but I am hoping it will be resurrected, though I have no idea on timescale.
I would suggest you +1 an existing bug, or open a new one… it may be closed as a duplicate but will register the point.
I am able to make the file uploads/downloads work if I remove the site url from the Admin->General line (only passed via the environment to the Docker setup) . However the thumbnails are still broken in the web client and the desktop client. The weird thing is that the Android client has no issues with the previews.
OK - there are a number of issue relating to this.
It is quite complex. Suffice to say as above support for sub directory/subpath installation was going to be pulled completely - and it has been neglected as a result.
The good news.
For a variety of reason there has been a change of direction and we are going to continue to support this.
I think your issue is likely here (there are several similar)
This is on the program to be fixed - quite probably in 3.16 but I don’t know for sure as yet.