Some TV Channels have been blocked / scrambled for the last week - i.e. TNT, USA and NAT GEO

Every time we try to access certain channels (i.e. TNT, USA, NAT GEO) the picture is scrambled and sound is choppy.  Anyone experiencing any similar issues and have any idea on what is causing this / how to correct it?  I've tried every troubleshooting recommendation provided by Xfinity, with no success.