I have a similar problem, with the only difference being, that the FP stays black (so no power button issue, I guess). I went to bed yesterday with at least 80 % battery and put it into airplane mode. In the morning the phone was empty (that never happened before) and now it won’t charge at all (?).
To be honest, my only concern is to get to my data on the phone. Since the update to the unified partition I was unable to access my internal storage, so I am lacking a proper back-up. Any suggestions for the battery issue? And any ideas concerning access to internal storage?