Oh my goodness! That is no good at all! Wiping the cache is a great first step but after such a large update, It might be worth it to back up the phone and do a full master reset. If the problems persist, we would need to look into replacement options.
My LG G6 has gotten a little warmer then normal a few times, the b8g problem I have experienced is an increase battery drain. This seems to be an issue with a variety of phones that got Oreo