The fsm workload random_moveChunk_refine_collection_shard_key.js and the two workoads that inherit from it allow migrations to fail with certain acceptable errors, but this check that a failed migration's error message contains a certain string is missing a > -1, which leads to a truthy value when the string is not present, leading the workloads to ignore more errors than was intended. This check should be fixed and any acceptable errors implicitly ignored because of this behavior should instead be explicitly ignored.