Overheating

I was getting the same on my first night of charging plus all of yesterday it kept getting very warm in the top right corner of screen today it seems to be settled down......so far

I have same issue. Also with iPad Air 2. It is charging very slowly and gets warm.

yeah i've noticed the slow charging on my iPhone 6 too

To me it's the bottom part of the phone that get's warmer, kind of worrying 😟 but "nice" to see that I'm not the only one 😉

There seems to be a lot of going on in the background after a fresh upgrade. Example: I had the Photos database filled with around 60.000 Photos and videos (optimized storage) and it took about half an hour before I could actually open the Photos app. Obviously cleaning up and deleting 100.000s of files in the background led to a very warm and slow device. It is now redownloading the thumbnails for all picture previews and it is responsive again.

iOS only allows cleanup and extensive sync-operations (backups, Photos sync, etc.) while charging, so that may be an explanation for your experience with overheating while charging.

This has happened with me on Every Device on Every Pre-Release. I think the statistics the devices gather is quite intensive, that would also explain the rapid battery drain when doing nothing.