If you didn't trash your old preferences when you updated to CC 2018 you should do so. I've seen several instances of what appeared to be bugs being fixed by trashing preferences.
To do so on a PC:
On Windows 7 and above the preference files are hidden. To find them go to the Control Panel and open Folder Options and then click the View tab. Then select “Show hidden files and folders” or “Show hidden files, folders or drive options” in Advanced Settings. Then delete (or rename) the folder at the end of this path: C:\Users\[User Name]\AppData\Roaming\Adobe\Adobe Illustrator [version number]\ Settings\<Language>. Make sure that Illustrator is closed when you do this. When you relaunch the program it will create new preference files and the program will be at its default settings.
I recommend that after you’ve reset preferences and have redone all of your settings as you like them that (after quitting the program) you make a copy of this new “pristine” version of your preference file and save it for future use. It is a big time saver to be able to trash preferences and replace them with a version that is already as you like them.