Repro:
Open vscode to a folder with a couple of ipynbs
As soon as vscode is up, start clicking on the ipynbs
Continue to click on them
In certain states (clicking fast seems to make it more likely) the webpanel can fail to load. In this scenario the file is then locked.

That failure is now cached and the file can never be opened unless you reload / shutdown vscode.
+1, I've encountered this randomly as well.
Yeah, I found it while trying to repro the "can't save" issue. This one I can repro pretty regularly though. Think that I see the issue as well.
Note for validation, the message still pops up. That seems to be coming from vscode and given our move to the new notebook editor I'm not sure that it's tracking down the root vscode cause. My fix here just prevents the "locked" state. That state was when the webpanel failed to load the host still existed and thought that it had a valid panel. So if you tried to reopen the file it would just try use the same panel and continually fail with the previous load promise.
Also started seeing this issue in the last few days. Version 1.47.2.
Version 1.47.2 This issue happens once I enabled Remote - WSL extension
I close the project folder and re-open the folder, it works!! (VS code, Windows 10, python project)
Validated. I can not cause the file to not be openable or uneditable (and I do get the webview disposed message)
Most helpful comment
+1, I've encountered this randomly as well.