During the chunk migration process, the source shard periodically polls the destination shard for updates. As part of the information verification process, we verify that the source shard's connection string hasn't changed. However, valid situations exist where it might change. For example, adding a new node to the source shard's replica set would change the connection string but would not change the behavior of that shard with regards to migrations.
Failures have cropped up where shards are aborted because the connection string has changed. Instead, we should verify that the from shard's name hasn't changed. Shard names are immutable and will serve to verify a shard without error.
The line of code to change is here.