Mongos unable to find document after migration
When querying with _id thru mongos, system directs that query to right node using config -databases chunks -collection information. It sounds like that "order" of your shards has been changed. (meaning that disk1 is not anymore at mongoshard1 -machine). Connect shard directly  and 

use local
db.me.find()

to check that nodes are who they should be.