My younger daughter's troubles with accidents (day and night) seemed to ebb and flow. Sometimes I could pinpoint the culprit (trips like camping at the beach would throw her off, for example) and other times it just simply seemed random. At 5yo we seem to be out of the woods as far as regression, but then I'll get complacent and she'll wet the bed. During the day I've tried to ignore her "potty dances" knowing that she *will* tell me when she needs to go. It is just so painful to watch the dance that I have a hard time not asking her "potty?" Mostly she manages it, then suddenly she doesn't for a few days. At night, like you said, it is because she is so sound asleep though she'll be OK for a while. Of course, when I leave the bed after they've fallen asleep, I'll scoot her right next to her sister (in my spot) and that is where the accidents happen!
So, it's possible that it is one thing that will pass (and of course it will eventually pass) or it will be like my daughter, coming and going for a while. When dd would have regular accidents at night I would wake her at 45min- 1hr after she dropped off. Even if she didn't pee this almost always helped.
We didn't do EC, but I would imagine that regression can still be an issue. Kids around that age really start to sleep deeply and for longer stretches, and it's the deep sleep that can be trouble, especially when combined with other triggers.
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