Hi, I just had this happen to me.
I'd just started using a new lens (50mm 1.8 STM) and tried different combinations of lenses, etc.
Both batteries I tested were full or near full.
Long story short: it turned out to be caused by the micro-SD card in a Transcend SD adapter! Once I'd taken that out and removed / replaced the battery, everything worked as before.
Really, really weird.