I have a QNAP also but I never link to it directly, just too slow even across 10Gbps LAN.
I keep 20TB RAID local for fast I/O, I wouldn’t recommend linking anything directly to a NAS. I know it’s done frequently but not advisable … use intermediary and then sync to NAS as needed.
Anyway, that aside, your QNAP drives will go into sleep mode and make take a few seconds to fire back up when being accessed, those few seconds could be why Ae thinks the drives are disconnected.
Do you have QTier enabled for any SSD drives you may have in your QNAP? Since SSDs don’t spool down they will always be ready for access.
With that said, if you are mapping a drive letter to the QNAP then you will need to add entry in your registry:
Add or edit entry “EnableLinkedConnections” (DWORD 32bit) and set value = 1 (Hex). This might help keep links active.