Maybe try to reload your cfg/ UI at Tools/ Customize/ Options >> UI >> Re-Load ( maybe load another one and then the one you normally use )
If that dont work, do a Repair
Next to try is delete the Built in, but then you can loose some settings on materials and you need to reload cfg and set template etc, run the wisard if you use metric system.
V18, V19, V20, V21, 2015/ 16/ 17/ 18 Pro. Platinum
Deluxe V20, V21, 2015/ 16/ 17
Windows 10 Home Premium 64 bit, 32 GB
NVIDIA Geforce GTX 780m, 1 GB