Screen keeps showing blue alert to please power off/on handset

My phone screen keeps turning itself on and displaying an alert that says please turn your handset off/ on and then two options at the bottom that say ok or cancel and at the top left there’s a back option. It doesn’t look very official and I don’t know why my phone would be giving me that alert. Next time it happens I’ll screenshot and upload it. Just a bit worried I’d been hacked and if I have what to do. Popped up twice- once when I was watching something and once when my screen was off it turned itself on to show it.