They've been confined for weeks under a COVID quarantine. With how long the lockdowns have been going on in China, I'm not surprised people are hitting their breaking point. Once you get to that point, it doesn't take much to break the proverbial camel's back, and messing with people's income is a surefire way to do it.
Regarding the financial status of Foxconn, I'm just firing out guesses here, but with how much Apple has cut back on iPhone production and lowered sales projections, etc., I wouldn't be surprised if they're feeling the pressure.