Sometimes won't charge when plugged in, gets hot

My Samsung Galaxy s6 intermittently won't charge when it's plugged in using the original or any charger. The phone gets warm, but the battery level doesn't increase. Restarting in safe mode and restarting again, or using a Qi wireless pad, worked for a week or two when it got balky. When it will charge, sometimes the rate is normal and other times it charges very slowly.

The problems seemed to start after the last software update on July 21st - but not immediately, since it's intermittent.

Today I'm struggling to get it to take any juice.

Is this a hardware or software issue?

Update: After safe mode and multiple restarts, it charged wirelessly. After a night turned off, it started charging when plugged in. Yesterday all seemed normal, but today it's back to making a chime and turning the screen on or off randomly.