Did you ever figure out the problem? I just ran into it myself and don't see anything obviously wrong. If I figure it out, I'll post again here with my findings.

I just figured it out in my case. Each of my two 2 VersionedSchemas, V1 and V2, was referring to its static models as [A.self, B.self], which is fine. But I had forgotten that I had also typealiased A and B to the current schema ("typealias A = V1.A"), which was overriding the static references. I fixed it by referring to the static models within the VersionedSchemas as [Self.A.self, Self.B.self], avoiding confusion with the typealiases.