Running GitLab CE 17.2.1 (Linux omnibus). Several users have uploaded avatars, and gravatar is disabled. On Code → Commits, uploaded avatars show correctly for all users. However, on Code → Repository graph, uploaded avatars work for some users but not others. For one user, the uploaded avatar only shows correctly if the commit email address uses all lower-case characters; otherwise a generic gravatar icon is displayed.
This mysteriously resolved itself after four days.