Had that problem before but after disabling all features I’m not using it seems to stop bugging me, I’m on v04.01.02-417 right now but problem gone earlier.
The only thing which still make me think of trying v3 is NFS which freeze if you try to download anything, but I’m not sure if v3 doesn’t have same issue.
Regarding downgrade, take a look here: http://community.wd.com/t5/WD-My-Cloud/Firmware-downgrade/m-p/693892/highlight/true#M9268
