I got a Fatal Error (500) when default branch from upstream is not present on fork.
It happened on rust2rpm repo: the main branch was created and set as default after I created my fork, it was master initially so my default branch was master and I didn't have any main branch.
I was unable to open a PR from my fork to upstream with the quick link where my repo appears (nothing displayed) so I tried to open a remote PR and I got a Fatal Error with the message: "Did not manage to rebase this pull-request"
Note that this happen even if I have the main branch but is not set as default on my fork.
The message was unhelpful and could be more explicit
Metadata Update from @ngompa: - Issue tagged with: bug