_mergeAuthzCollections is an internal command, which performs a very specific, and expensive, operation for mongorestore.

mongos may attach a MaxTimeMS to this command, when it proxies it to the config servers. This can cause restoring many user documents to fail.

Because _mergeAuthzCollections is internal, requires extensive privileges, performs an intentionally expensive operation, and failing due to timeout seems undesirable, it should ignore MaxTimeMS.