I have just tired to migrate from OS 3 to OS5 for my WD My Cloud 4 TB. After upgrade ( which was bumpy) , it said that internal error 500 ( my internal ip of device is not accessible).
via mycloud.com or WD app or View public page option - it is not accessible.
However I am able to access the drive by maping it as a network drive. ( Best part of this upgrade)
I have tried 2 times restart … nothing changed. There is no light at front of the hard disk ( I do not think that I can call it NAS).