It’s similar to this and this. Basically the default Jira “user picker” field works but when we added another same “user picker” field as “assignee” (required) then we have such issue (no drop down user selection). For date issue I think this pull request fixes it.
Another issue is that if we set the field to optional but Sentry still requires such field - similar to this.
We are on Chrome Version 78.0.3904.108 (Official Build) (64-bit)