Hello!
Now, this is not a 'fix' per se, but a consistently effective work around:
Keep the lid of the APP case open while charging the pods! Charging proceeds in good order, without the appearance of sudden % drop. This works with case wired or not.
I use a small microfiber cleaning cloth to keep the snappy lid propped open.
Apple is sending a replacement case to me; I'm eager to try it out. Will post experience here.
(I did try resetting the APPs, as well as Mimiron's full drain suggestion, to no effect.)
Best,
KM