It's most unlikely that the firmware update made any changes to the camera's properties.
If it did, DJI would have trumpeted that.
It's very rare that firmware updates make any differences to anything that users would notice.
The exposure issue won't be related to the heat or battery issue.
But if you upload an original jpg to Google drive and post a link, someone might be able to check to see what might have happened there.
It looks like you've almost gone to the...
What were you using to plan and fly the mapping mission?
Before RTH drones were available, you could produce reasonably accurate maps with the Phantom 4 pro, but easier than with a Mavic 3 pro because you could use apps like DroneDeploy to plan...