I've also confirmed that the same issue occurs on 26.4 beta 2 and beta 3.

Unfortunately, I don't have a way to reproduce this 100% reliably, but here are the steps that most often trigger it: Set up the usage limit first — configure a usage time limit of 1 minute or more before connecting the charger. Then plug the iPhone into a charger — the issue tends to appear shortly after charging begins. That said, it seems to only trigger once per day — I haven't been able to get it to fire a second time on the same day. Device model: iPhone 16 iOS build: 23E5223f