If the cable provider flagged the program with one of the CCI bits set, the stream is encrypted and Myth cannot handle it.
Comcast users are generally not affected all that much, only the premiums and movie channels are copy-once.
Verizon FIOS users are not affected at all, nothing is flagged.
Time Warner and Brighthouse flag everything except the locals so it's almost worthless for them without WMC.
Everything else is a mixed bag.