Not a solution, but I am also having problems with SEO's..
This happens to be an AC12 file, but it would seem you can reach a limit (might be based on available RAM)...
But I have a complex profile that I am using for a BASE on walls. It has a REVEAL in it, so I make it coincident with the wall and SUBTRACT w/ DOWNWARD EXTRUSION to cut the bottom of the wall away..
Works great about 90% of the time, but as the file grows larger and I try to create additional SEO's, the simply DON'T work... Same 2 pieces (complex base and traditional wall)...
Anyway... Not sure what the answer is...
Duane
Visual Frontiers
AC25 :|: AC26 :|: AC27
:|: Enscape3.4:|:TwinMotion
DellXPS 4.7ghz i7:|: 8gb GPU 1070ti / Alienware M18 Laptop