Enabling Geo sharding on collection with 20+ million documents

We are testing enabling geo sharding on our database. When we enable sharding on the collection that is already populated with the documents (20 million+) we see that one shard doesn’t split the chunks properly and hold 300MiB of data per chunk while the other has a proper chunk size of 32MiB. But when we drop the collection and enable sharding on the empty collection and then restore the data it split properly both shards have 32MiB per chunk.

This brings me to my question, is there a limit to how many documents the balancer can move? Our shard key has had no issues when we restore to the empty collection.

We are using MongoDB v4.4.9