In my case these were all the steps (not a minimal repro):

1. Have a bunch of branches from the extensions
2. Execute the Delete local branches and remotes command
3. Select all and delete

...wait... it did not terminate after several minutes

4. Reload window
5. Repeat 1 - 4
6. Execute the command again but select 1 branch.

🐛 => notice that the command hangs and Git output channel says the branch does not exist (which is true)