It is happening with me. The phone gets warm, not hot with normal usage and battery drains faster. Then i restart the phone and temperature goes down. I think this is happening because of some app running itself in background and restarting stops it.
One thing i can say that the battery optimisation feature which tells about app draining more battery is not working properly.
Try to find apps you may have installed recently which need to run in background like Skype or Outlook. Uninstall them and check if there is any improvement.