When the CollectionCloner fails, the status is placed into _failedNamespaces here. However, we never do anything with _failedNamespaces besides check and print its size. We should print some, if not all, of the errors in the CollectionCloner, especially now that we don't do any collection cloning in parallel.

Another solution would be to print CollectionCloner errors at a log level greater than 1: https://github.com/mongodb/mongo/blob/726cafd713c7333640f8458ec9808ed4f678e3a7/src/mongo/db/repl/collection_cloner.cpp#L542