I did a little research on this problem and it is a Linux design issue. For example to find out the size of a mounted device, UD uses df on the mount point. If df is run on a mounted device that is off-line it will hang (this is by design) waiting for the device to come back on-line. I did what I could for the SMB shares by not doing things like a df on it if UD sees that it is off-line. It would be very unwieldy to try to cover all the cases, and I don't have any interest in doing anything further with LT saying they will fold UD into unRAID.
My suggestion is to not mount SMB shares in unRAID for extended time periods, and if you do be sure the mount stays on-line. Why mount an SMB share in unRAID to then just share it again as an SMB share? If you are sharing SMB shares with NFS on unRAID, I'd suggest another answer.