QNAP 431 fails file system check - what to do?

Question

NAS

After power loss booted as usual with file system not clean. Usually I pressed check and after half an hour everything is ok.
Now hangs at 9.3%. Overloaded 10 times.
If I try stop check - it hangs on stopping.
The files are available. Raid5 4x4tb.
Nothing through ssh at all. /dev/mapper/cachedev1 busy even after umount -l

Answer 1

Topic closed. Firmware 4.4.2 buggy, withdrawn. Downgrade decided.