Export UV maps to Alembic on every frame. This makes the export of UV maps consistent with mesh normals. In the case of static UV maps it may cause a slight slowdown (since they're exported on every frame now), but due to the deduplication performed by the Alembic library, the resulting files will be the same size anyway. Thanks to @CodyWinch for providing the solution to the problem, and writing the original patch D8397. Differential Revision: https://developer.blender.org/D8397