It could be just that, you may want to disable that if you only have one redis endpoint. Since the endpoint will be handling the slot hashing for you.
AWS Elasticache has two ways of running Redis, a redis DB server with slaves and multi-AZ failover, and redis in cluster mode, which is a proper redis cluster as is described byt he redis documentation.
The error is being generated from Redis and basically says “The key you are looking for is not on this server”, but if you have only one redis endpoint configured in Tyk, it has no choice but to access that server.
Have you tried that?