I recall this problem before with
VTV4 and missing audio. Some receivers picked it up, others didn't. Apparently the uplinker changed the APID settings for VTV4. So when you rescanned some receivers it lost audio -- interesting thing was that other brands of receivers worked fine. We all went nuts trying to figure out why this was happening. Eventually the uplinker changed the settings back to their original configurations and all was good again.
In the meantime, if your receivers allows it, try setting the transponder configuration to "AUTO PID" - some receivers have this feature; EmTech does. I'm not sure about Fortec. Then do a rescan of the 12,177 MHz transponder.
Keep us posted on your results because this is very interesting.
kat