Same problem here too, damn dulan...the original S View cover no such problem.
There is definitely some issue with the Slim Armor View case.
I changed 4 sets from the shop over a span of 3 days. Damn frustrating.
First set, the sleep mode failed to work. Quickly walked back to the shop to change another one.
Second set, the sleep mode failed to work most of the time. Had to take the phone out of the case, adjust the pins, then put it back only to fail again after a few hours.
Third set same issue.
Fourth set same issue.
Damn dulan, gave it to my friend for free who is now encountering the same issue.
Yes, no issue with the original Samsung S-View cover here too