I would first check the file server that is running very slowly for hanging Disk Agent processes. Go into Task Manager, get a list of running processes, and look for any of these
vbda
vrda
ob2bar
If you see any, then kill them. I have seen cases where a backup failed, and left behind a Disk Agent (vbda) process. Other vbda processes start piling up behind, and backup runs slower and slower, until it stops altogether
I also advise that you go to the Options tab, click on File System -> Advanced button, and enable Display Statistical Info' so that you can see if it is just one or two objects that are running slow
TRying to diagnose performance issues is very difficult because there are so many possible variables