I did a DFU restore. Setup the device as new. Reinstalled everything back to the way it was with the only exception being that I didn’t install Dropbox and Google Drive. Everything works well now. No battery drain for the last two weeks.
Since yesterday I'm talking to Apple because I have similar issues on 1 year old iPad Pro . There are times where even if connected to its original charger, doesn't charge and I need to restart or force restart to have it charging. Many times it showing that it charges till 94% and no more. At restart actually it's even less. I sent all the battery screenshots at the Apple representative : activity, percentage 24 Hours and 10 days etc. What it's really weird it's that even on the charger it using the battery, as you can see on the screenshot. All this happening since installing 13.5 and worsening since 13.5.1