I was having the same issue with my right earpod and when you put it into its case, sometimes tried to charge, sometimes it just don't... as being someone with OCD and always cleaning the unit, i took a look inside the case with a fiber optic camera probe and, as you can barely see without it, it has 2 contact points in the case for each earpod, turns out that (seeing it with the probe cam) one of the contacts is peeling (because it is not pure copper, or assuming, because pure copper doesn't peel)
Tried my best to clear and put a micro layer of copper and, at least for now, works.
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You can see the black dot int he picture (sorry but couldn't get to focus inside)
This will be not really helpful but informative.
I was having the same issue with my right earpod and when you put it into its case, sometimes tried to charge, sometimes it just don't... as being someone with OCD and always cleaning the unit, i took a look inside the case with a fiber optic camera probe and, as you can barely see without it, it has 2 contact points in the case for each earpod, turns out that (seeing it with the probe cam) one of the contacts is peeling (because it is not pure copper, or assuming, because pure copper doesn't peel)
Tried my best to clear and put a micro layer of copper and, at least for now, works.