We recently upgraded Jira Server to version 9.3.0 and have been experiencing some odd issues.
In one of our projects (possibly others), users are not able to inline edit the Assignee field from the issue View screen, but only for some issues. I have been able to reproduce the problem as a Jira admin, so it is not a restriction on users. I have also confirmed that the Assignee field is part of all screen schemes used by the project.
There doesn't appear to be any pattern to which issues have the problem, and I do not get any pop-up messages recommending a re-index. Any ideas what could be happening?