My sony ex1 is over 5 years old. Normally it works fine. I can use it for two or three hours in the outdoor heat, temps to 90 ish. I then bring it indoors and when it powers-up it has an unusable registration-bad image. About an hour later it will power-up and be fine for hours after that. This is not the lense getting cold and condensate forming that we can see. If I don't let the power go off, i.e. change batteries with a power source plugged in, the problem will not appear at all.
It seems to be an init issue. The text in the viewfinder is always fine and clear. The image recorded contains the horribly registered images.
This has been a problem for a good year now. I have to run a backup camera during the 'bad hour'

Is this backfocus or the sensors?

The backfocus problem is common on EX1s that have had more heavy use. You could try updating your firmware at a Sony Service center. (If it's a really old firmware)