Charging case charging backwards

I have a charging case for my iPhone 11 Pro Max. I’ve had it for a few months now and while it’s had a litany of issues, this one is the most unavoidable. I charge up both case and phone every night, but for the past couple of days, my case will stay at 100% while my phone battery dies within a few hours. It seems as if the phone is charging the case and not the case charging the phone. Any suggestions?