Potty training regression?

My boys will be 4 in May and have been potty trained since last June. Accidents here and there. The past few weeks they’ve both multiple poop accidents. It started with one and the other followed. They were so good about letting me know when they had to go so I’m so confused what happened. I’m throwing out so much underwear.

I don’t know how to handle this. I’ve been on their case a bit about if they have to potty because the accidents are so frequent. They get defensive and a half hour later they are walking around with poop. A few times I think they didn’t want to stop playing to get up to go because they didn’t want to miss anything.

I usually have a talk with them and get on their level. Today it was back to back and I was frustrated. I yelled at them and I feel so bad.

Anyone have any advice? A few of my friends said their kids also went through a regression like this.