@baumgarj Actually, I found the problem. It seems like parental controls were set to "Bedtime" from 12:00 to 5:00, The problem is that I never set any of this up. Is this the default setting?

I have a Deco X55 Mesh system with 3 units. Each night (midnight) my iPhone gets a browser page labeled "TP-Link Parental Controls" with a message: Time is up! You have used up your online time for...