Sorry that didn't quite work. There are still a few more things we can try that I was hoping to avoid since they require some resets.
When Attribute Assistant installs, it generates a configuration file which tells the tool how to behave. If you navigate to 'C:\Users\<USERNAME>\AppData\Roaming\ArcGISSolutions\ConfigFiles' you should see a file named 'loaded.aa.config'. If you delete this file, ArcGIS will recreate a new copy on the next load of the program. I'd suggest rebooting your machine before the restart just to get everything cleared up.
If that still doesn't work, you can do a soft reset of ArcMap. This will reset all of your toolbars and mxd preferences, so I suggest taking screen shots to make sure you remember what you have. If you navigate to 'C:\Users\<USERNAME>\AppData\Roaming\Esri\Desktop10.6\ArcMap\Templates' you will find a file named 'Normal.mxt'. This is the template that ArcMap updates every time you save, open, or close the program. If you rename this to 'Normal_old.mxt', it will disconnect it from the program. When ArcMap is rebooted, it will recreate this file. Once again, I'd suggest a reboot between renaming and restarting ArcMap.
Andy
Andy Shoemaker