Web app stops working after adding a new environmental variable.

I have a python web app deployed on a linux machine. In the Azure Portal, for this web app I set a new environmental variable. It is not referenced in the code and does not conflict with any of the azure names. Once I save the new environmental variable, the app page shows an Application Error. The diagnostic report says "Resource not found". The "self-diagnostics" do not pick up any issues (all tests complete and show a green tick).

The app was working fine before the variable was added. Stopping and restarting the app does not fix the issue. Restarting the app does not fix the issue. I have to do a full redeploy to fix the issue