UPDATES:
When I open the Source Control panel in VScode, normally I am able to see any diffs and at the bottom of the panel I can open/close various tabs such as Commits, Branches, Remotes etc. These tabs have all disappeared for a specific repo.
Here is how it should look:
However, they are not showing on this specific repo. Here's how it looks on the repo in question:
It was down to not having Gitlens enabled in the workspace 😬