Hi Mate
I have had similar issues with the lower joint on my LH ring finger, joint feels sore at sides but not top or bottom, not sure what caused it but it appeared after a session on tweaky plastic, odd sideways movement of the joint may be responsible as have had similar before when crimping hard on a low start and moving sideways/reaching
Oddly I can crimp OK and Open hand/slopers etc, just certain pinch positions are painful!
I have found using Ibuprofen for a couple of days alleviated most of the soreness/inflamation and I use icing now if I suspect tendon or similar tweaks, this has helped considerably as has reverting to gentle open hand training and easy trad for a couple of weeks - in my case age (48) may not be helping the joint's general health
If you consult anyone I would be very interested to hear what they have to say
Good luck, H