"Source branch does not exist" when it actually exists
Summary
MR widget displays Source branch does not exist. Please restore it or use a different source branch
when the branch actually exists. The same MR displays the diff
correctly.
Steps to reproduce
Unfortunately, the issue is transient, although the customer says that it sometimes happens for them.
UPDATE: https://gitlab.com/gitlab-org/gitlab/-/issues/439613 has recent logs
Example Project
See the details in this internal ticket: https://gitlab.zendesk.com/agent/tickets/256583
What is the current bug behavior?
Merge Request cannot be merged because it erroneously displays Source branch does not exist. Please restore it or use a different source branch
What is the expected correct behavior?
Merge button should be active and there should be no Source branch does not exist. Please restore it or use a different source branch
message.
Relevant logs and/or screenshots
I have found the branch push event in logs. In Gitaly logs this event has mention that PostReceive hook failed with the following error:
GitLab: Http post to GitLab API/post_receive endpoint: Internal API error (503)
Output of checks
This bug happens on GitLab.com