Since I updated from Vegas Pro 16 to 17, I have not been able to use my FX Home HitFilm 360 Pack plugins. They are there and working fine in 16 but can't get up in 17. I sure am not going to upgrade to 18 if I can't get any help with this.
I had this issue upgrading from MEP to Video Pro X today. I had a folder in “Extra FX” that had my missing plugins. Very possible you may need to simply try to reinstall the HitFilm plugins from the install package.