I don't know if this is specific to my pull request but on PR #2558 I'm seeing:
fatal: Invalid symmetric difference expression 49f6449ef4b81537c19b82329caaf60596c516c2...7b634956246bc6112a16ba11ff9f721342e750e6
Only docs were updated, stopping build process.
The build is subsequently marked as green. This is invalid, there were code changes in the pull request.