So when I join any server, I download files. And when I join this server again I download the same files again, and again, and again. What could be the problem?
The servers fastDL has been incorrectly set up. Problem at their end, not yours.
To be put technically in case you want to forward it onto the server owners, They have a fast dl URL but haven’t uploaded the files either correctly or at all. If it’s .lua files, they need to send the cache over to the fast download too.