dencal said:
PSGS
It could be that the connection with the Samsung was a bit dodgy, as the SKHynix is now working using the same connection.

Am pleased to see you are now reaping the benefit from the superior 850 Pro SSD.
Yes, there must have been a bad connection. I am still running at SATA III, without any fall-back until now. So I guess my problem is solved.
I hope the threat starter was lucky too.