I understand how frustrating it is, when you came back to play, doing everything correctly, however, suddenly had an injury.
Do you happen to have a virus infection or cold recently? Once I had a strange joint pain, level 6 out of 10. I thought it was an injury, and started to read books about injury and piano technique. That was actually time I really learned how to play with arm weight, wrist circle and forearm rotation.
Gradually I recovered and made great progress. A few months early, the joint pain happened again, but this time I realized I caught a virus, which was not just coincidence. I believe the virus triggered inflammation and the pain. Once I recovered from the virus, the pain is gone.
Hope you will recover soon.