I believe coincidences are rare. My suspicion is that when they worked on
the charging problem, they removed the flywheel (am I correct to assume this
would be done?) and never tightened it afterwards. Would a loose flywheel
cause the problem I've experienced? Could running with the flywheel loose
damage the fit where it can't be tightened properly, and the problem
continues?

If the flywheel was loose enough, there is a possibility that it wasn't seated
in the keyway. The flywheel could cause the engine to be out of time. If so it
would or could be retarded enough to not get full power.

Leanne