this is a problem with a test and not the server itself.

https://github.com/10gen/mongo/blob/master/jstests/serverless/shard_split_change_collections_test.js#L103 we do a drop after we forget the split operation with `operation.forget()` but the code doesn't wait for the access blockers to be cleaned up after the forget operation so its possible they could still be in place. this drop failed in a patch build i ran so i noticed it, but I haven't seen it fail in the waterfall.