Blame it on the rains, if you got a 90cm dish, then you are on Ku band which gets affected by rain(rain fade). Also, DSTV signals are beamed from W7 satellite but different transponders so that could be related to specific transponders being down.
If the problem persists, try re-aligning the dish if no much change, guess your LNB has partially failed hence cant receive certain frequencies.
Disclaimer:
I dont work for DSTV but Dr. Google is a good friend.