When two keys have to be inserted by the config server primary, it does so serially, so there can be a delay between creating the first and second keys. mongos_does_not_gossip_logical_time_without_keys.js asserts there are at least two keys after it has received a signed logical time in the response from mongos, but it's possible mongos has only read the first key from the config servers, and this assertion could fail even though the second key is about to finish being inserted.