This might be a good advice in some cases (and -- for the "Extremely unprofessional" part, a somehow good judgment but applying to slightly different situations), but I think you are missing tons of context here: see the openly discussed details already linked in other comments: https://gitlab.com/gitlab-com/www-gitlab-com/issues/5555#not... https://gitlab.com/gitlab-com/www-gitlab-com/issues/5555#not...

Apparently, Gitlab operate very openly about even that kind of sensitive matter. In that situation, the whole openness would make absolutely no sense if you can't disagree in the tracking system actually used to communicate. In the context of all the details already published by all parties because of the company policy, the resignation sentence is completely benign.