They are - the TTI STI 9mm Follower.
They are hanging up on the cutouts at the front of the mag - only on the way down, and only on one side.
Today I placed an order for three (needed four, but sold out) of the TTI Ultimate SV/ST Universal Follower thinking that perhaps the STI follower isn't meant for SVI mags.
Any help you can provide would be appreciated.
(I also submitted an inquiry via the website - which you can ignore if you have a solution here.)