I also have just observed this issue when updating a PR with a second commit.
Refreshing the page or editing the PR (as suggested in the error message: "Try refreshing this page or editing the pull request directly") does not resolve the issue.
Same problem here ;-)
Tried to merge a PR, then it failed. After that, I cannot access to branches view or merge any PR.
Jesus! I have failed in creating PR over and over again and I got this 'Something went wrong while creating your pull request.'.