mongorestore not sharding data correctly and there are errors in the mongos log

Wed Jul 10 09:08:57 [conn167] warning: splitChunk failed - cmd:
errmsg: "the collection's metadata lock is taken", ok: 0.0 }

I stopped the mongorestore after a while and have wait since to see if the balancer would move chunks around but nothing has happened.

Balancer is running.
db.locks.find() returns nothing

Any ideas why it has not sharded the data? Should it have during the restore?

The shard key will contain strings

When creating the the 3 chunks it has created them as
minkey -> A
A-Z
Z-> maxkey

this explains why all data is in chunk 2 but after 10GB of data I would have expected A-Z to split by now. We have a large distribution of values and our chunk size is 256MB