Devcontainer does not run `postCreateCommand` for some users

We've noticed this with a couple of users, I have noticed it on my laptop but not my Diamond workstation. The expected flow is:
1. Container builds
2. Displays a message saying build is complete
3. Runs `postCreateCommand` and begins installing dependencies etc.
4. Displays a message saying devcontainer is ready and that the user should press any key to continue

The observed symptoms are vscode getting stuck at step 2. reloading the window usually gets it unstuck and it executes step 3. and 4. more investigation is needed