This seemed odd, but I didn't really put much time into trying to figure it out.
Recently in the Zhumell Customization thread over on CN, it was mentioned that the bottom screw in the focuser isn't really needed, and it prevents the focuser from reaching full travel.
I pulled the screw completely out for my most recent session, and sure enough, the 18mm can come to focus without the extension tube
I am going to run on the assumption I played with the screw at some point, and since I didn't think it mattered, it didn't occur that it was an issue.
With the screw removed, I do not have to worry about it happening again
{I think this is the locking screw}