Well, I tried approach 18C at LTAI with Laminar Research B738, first with Navigraph navdata update, then with Lamninar research default navdata only. Everything was fine, as you can see on this screenshot :
https://www.dropbox.com/s/6ynyek46nvjvy4s/LTAI%20rwy18C.jpg?dl=0
I suggest you launch the installer to either update or check if any file needs to be repaired.
If no improvement, try and delete (or move for backup) your X-plane 11\Output\Preferences folder. You will need to restore your settings after that.
Any feedback will be highly appreciated, that's all we can say for now, without your log.txt.
Regards,
Guillaume