Preview broken?

I’m having a strange behaviour on my mobile editor preview. No matter what view I’m previewing, it shows a blank page with the app logo in the middle. Refreshing the editor and relaunching the browser won’t fix it. It has not always been like this (it used to happen occasionally but would go back to normal on its own, now it seems stuck like this).

The app shows well in BubbleGo.

Any fix for this?