Ok. I’m not really and expert when it comes to those electronics and components. @las isn’t called Dr. Scisky without reasons. I’m just a user with some (very) basic understanding of that stuff.
Sounds like a damaged fet. But why? S3 solder joints seem not to be bridged on the upper side. Don’t know how the underside looks.
What is that white stuff in between S3 + and - ?
But bare wires of motors are very long. In a crash it’s possible that they get contact to each other or the solder joints and produce a short.
Did you fly it yesterday after the bypass surgery? If yes, did it work properly?
If those wires produced a short and damaged the fet normally this would be recognisable immediately. But if contact was really short, maybe the fet didn’t get damaged completely but died today.
Just my theory, not sure if this makes sense.
Your picture isn’t that good to zoom in and see details.
Fet on S1 have a blob/bubble on top, maybe glue residues. But no problem with that motor, right?
What about fet on S3? Does it looks burned? Bubbles or blisters visible? Smell?