I cannot provide a link since it runs on localhost, but whenever the auto complete field is used, I get loading failed. The only cause I can think of is the fact I recently changed my forum tables to utf8mb4.
EDIT: I now consider this a bug as I'm still having this problem even after reverting my database before the table encoding change.
bump - Also seems to be messing up my quick edit too. Originally I thought it was my hierarchy plugin, but have it disabled and still problem persists.
Moved by Ircher's request based on the nature of this appearing to be a potential bug.
Some more info on what I've discovered:
I have found the problem with the username autocomplete - Apparently, the MyPermissions Plugin is the cause (just tested on a new forum); however, this incompatibility must be a result of mybb 1.8.4
I will look into quick edit now.....
I can now confirm both problems are caused by the myPermissions plugin. Perhaps Pirato Nervo (don't remember updated name) should look into it? The plugin worked fine before mybb 1.8.4...