I have the following line at the bottom of my .zshrc file:
bash ${HOME}/.asdf/plugins/dart/tools/dart_version_watcher.sh
I didn't notice a problem for a while (due to my penchant to not close VS Code windows very often), but when starting up VS Code after a computer reboot, the shell environment took a while to initialize, after which I got a message saying "Unable to resolve your shell environment in a reasonable time. Please review your shell configuration." After that point, the integrated terminal was frozen on "Starting" no matter what I did. After some investigation, I narrowed the cause down to the above command.
Note that this only happens when VS Code is first starting up. If I comment that line and start up VS Code, then uncomment the line and refresh the integrated terminal with the zsh command, the terminal successfully refreshes.