Checking out a remote branch and de-selecting "Local branch should track remote branch" will prevent you from tracking the remote branch later.

Steps to reproduce:

• Have a remote branch without a local branch
• Check out the remote branch (either right click the remote branch in the sidebar or right-click on the latest remote branch commit and select "Checkout")
• In the pop-up dialog, uncheck "Local branch should track remote branch" and select "OK"
• Now we have an untracked local branch
• Now right click the local branch in the sidebar and hover over "track remote branch"
• All of the options are grayed out and "(None)" is selected