New issue on assignee list doesn't get created

Summary

I'm having the issues for group board (Self-hosted GitLab Enterprise Edition 11.10.4-ee). Sub-problem of #11021 (closed), ping @smcgivern.

Steps to reproduce

Have board where lists are divided by assignee (label and milestone lists not affected). Click "+" button at top of list to create new issue. Issue will disappear and won't be created in first place. Workaround: use other means to create issue.

@smcgivern : I cannot reproduce this 🤔 Can you show this in a public group on GitLab.com, please?

I forgot to mention that board scope was set to milestone "Started". I can't reproduce a similar setup on public gitlab (GitLab Enterprise Edition 11.11.0-ee), but bug is still present on our internal self-hosted gitlab (GitLab Enterprise Edition 11.10.4-ee). Either that's versions, or some milestone setup behind the scenes.