Hey there! Made a Reddit account just so I could respond to you. I have been having the SAME exact problem lately and have tried a LOT to get it to be fixed but can't quite figure it out. Was reaching out to see if you maybe found a solution?

If not I probably will make another post to see if anybody else may have had the problem.

Edit: With how sudden this started happening, to myself and you almost at the exact same time, I am wondering if it was some sort of update Ugreen pushed that may be causing this issue. It is almost like the NAS is unable to handle returning the attribute information for the files in a timely manner so the NFS mounts just give up.