This feels similar to MC-266543, but I couldn't tell whether or not this part of the issue was resolved, and if this is an intended feature, it is a very strange one. Any mobs ridden while [/tick freeze] is active will move, and therefore not be frozen.

           How to Reproduce Issue

1. Spawn rideable entity (horse, pig, llama, or if your really fancy, use [/ride] on another entity)
2. Run the [/tick freeze] command
3. Ride the entity and notice how it is not frozen
4. Dismount entity and note how the entity re-freezes
5. Run the [/tick unfreeze] command and note how the entity then moves normally