Hi I have the exact same Problem!!

I use python and marimo in a uv env in my workspace Folder (Win11) . And get the same marimo not loading problem and want to share some Additional information, that could maybe help:

screenshot

Basically it seems the ports of the marimo server, the marimo VSCode extention and the native VSCode notebook editor do not match up. When I change the port in the marimo VSCode Extention from 2818 to 2819, the marimo server starts on port 2820, but not always, it seems the port difference of 1 between settings and marimo server start is only happening sporadically.

I managed to at one point get all ports to match up, but still had the same issue:

screenshot2

Also restarting my PC, VSCode, it's extentions, or marimo did not work for me.