Guided access Ipad: Weird screen form in grey appears

Hey all,

Somehow I feel that Apple wants to hold me back from using my ipad as a wall mounted dashboard, so I need your help to prove me wrong.
I use an Ipad Pro in a wall mount in my living room. I´ve put it to guided access mode and ensure wakeup with notifications sent via a presence sensor. That all works as it should.
But since some weeks I have this weird issue, that when I switch on guided access on the ipad, it shows this weird grey form on the screen. Once i turn off the guided access, this disappears. The form keeps changing all the time I activate guided access.
Anyone an idea, how to resolve this?