No power to switch box and overhead fans/lights in master bed/bath. No tripped GFCI, no tripped breakers
Except for certain code-required dedicated circuits (mostly kitchen, bathroom, laundry), you can have a lot of stuff on one circuit. That is especially true these days with LED lights, but even in the old days. 1/2 my house - lights in 2 bedrooms, receptacles in 1 bedroom, lights and cooktop exhaust fan in the kitchen, several receptacles and some of the lights in the basement - are all on 1 15A circuit!
When only one part of it goes bad, the problem is either in the first part that is bad or the last part that is good. You have determined the switch is OK because you have no power on the wires. So you have to trace it backwards to figure out where it came from. You likely have a loose wire, open wire, bad receptacle or bad switch. Check especially for any &quot;back stab&quot; connections.
What caused it? You might figure out when you find the problem. But since you already had 2 broken switches, I wouldn't be surprised if you find more things broken or about to break. It is quite possible that when you or Comcast was doing some work, you pushed something &quot;over the edge&quot;.