not sure what you are building but i hope that was for a real time multiplayer game otherwise doesn't make sense to have bi-directional communication when you only need reads

making read replicas function also as writes is needed for such cases but already when you have more than one place to write you run into edge cases and complexities in debugging

I think the reason is pushes are sent out regularly in batches by some cron system and rather than reading from the main database it reads from the replica before it pushes them out. I didn't really explain the context properly in my comment.