sideload for personal failed

I am having problems sideloading a custom app for Microsoft Teams. I am testing with a new personal app which is failing to load with the error  "sideload for personal failed" (see attached screenshot). The app seems to work initially and then fail for now reason. I've tested a number of times and am getting the same behaviour when debugging in VS Code or when sideloading using the downloaded publishing package.

Can someone help to troubleshoot please?

Thanks!