Invalid index & data size after sharding collection

The index & data size for the newly sharded collection is invalid and unevenly distributed among shards.

I have a collection that has index size=60.208GB before sharding. The index distribution after sharding looks like below:

Shard1: 57.465GB
Shard2: 90.855GB

Also, data size seems to be reported invalid:

Data size before shard: 861.643GB
Data Size Shard 1: mydb 623.69GB
Data Size Shard 2: mydb 430.835GB

Data size shown in mongos for db mydb:
mydb 473.019GB

MongoDB Version: 4.2.6
Shards: 2

What might be causing this imbalanced data & index sizes on shard?

Thanks in advance!