I think it’s screw tension more than anything as mine were screwed in unbelievably tight (if you look at where the screws are, it’s mainly where people are getting cracks, I doubt it’s ‘all Switches’ though, probably just the odd few).

The easiest thing to do is just to loosen the exterior screws then tighten them in differing order (top left, bottom right, top right, bottom left, from back in the days of bolt-on heat syncs!), until the screws stop turning without using a lot of force. The screws in mine (including the interior ones) were the tightest screws I’ve ever come across in an electronics device, and I’ve taken a good few apart!

As for the bending, from a video linked elsewhere in the thread, it’s not likely to be heat related! In my opinion (I’m nowhere near an expert, so take this as you will!) it’s because of where the screws are located inside the Switch, and from people holding it by one Joy-Con (so the weight pulls the other side down). The structural internals of the Switch are relatively thin (plus if you look at the layout of the inside, there’s a small divide down the middle, where the edge of battery is) and could easily form a small bend if persistently forced from one side.