Gravity movement works perfect here with A8.

IN_SOLID and the other flags were for AABB collision I think, they work only in A6 levels. In A7 and A8, you have OBB collision. You use the CONTACT struct with A7, not IN_SOLID.

That was probably the mistake. A6 levels and AABB was still supported in A7, but not in A8. Just compile your levels to A7 meshes and use CONTACT and everything is fine.