System ui stopped when using custom notification

I tried the new notification feature with one of the provided examples. After around 10 minutes of it working fine a window popped up reading "system ui stopped". It seemed like it repeatedly failed to load the background (the screen loaded and went black again)...I could not use my phone anymore. Luckily I managed to access the kustom configuration file via my PC and deactivated the notification. After rebooting everything worked fine again.