Another bug "the project is already open elsewhere"

The error - in a red warning box - occasionally appears in the Makecode editor.

In connection with the bug I just descibed a few minutes ago, I just tried edtiing my main extension from within the project. I was not editing the second extension (an extension on which the main extension is dependent). When I edited the main extension’s .ts file I got the error message. I went back to the editor home page and selected the main extension to edit it independent of the project. When I did this and then went back to the project, the Makecode editor hung up indefinitely.

Project code lost forever, again, because it’s impossible to reload.

Could you open the javascript console in the developer tools and copy the stack trace where we fail to load the corrupted project?

Are you referring to Firefox’s Web developer console? If so, where do I find the stack trace?

In firefox, go to the hamburger menu -> Web Developer -> Web Console.