This has been there for years and years, since I started AppSheet in 2017, but not being corrected at all unfortunately.
There is option called "Pause App" in Manage > Deploy > Pause App.
This function is believed to be prepared for App Creators to let the app users not to able to edit the app while the App Creators made a modifications to the app due to maintanance, upgrate or whatsoever reasons. However, as soon as we turn on this option, even the app owners are not able to view the app even through the PREVIEW in editor. Hence, as far as I believe nobody never used this feature.
Once the option is turned on, the app owner is alos ruled out to view the app through the preview. Then question is what is the purpose of this particular feature then?
De-fact, this seems to be a bug as it is perfectly illogical.....
Hope AppSheet/Google team would review such an important feature. ...