Why can't some Redis instances use the KEYS command?

For Redis instances with sharding cluster enabled, if the keys to be operated by the command are not distributed in one hash slot, the error CROSSSLOT Keys in

Hash tags are a way to ensure that multiple keys are allocated in the same hash slot The error includes the hash slot of the key and the

error slot shows you why you get the CROSSSLOT Keys in request don't hash to the same slot

error_ replication slot is active for pid shows you why you get the CROSSSLOT Keys in request don't hash to the same slot