Unable to connect to redis sentinel through kubernetes

I've updated to the latest stackExchange Redis, this configuration used to work but now I've received this error.

I've removed commandMap as suggested in another issue. I've made sure all the ports are open.

Not sure what I'm doing wrong here... This is running in k8s

I've tried stepping through and debugging, however it looks like the Standalone type is just defaulted then I can't spot where it would be properly swapped to sentinel... If you could explain how this works to me then I might be able to debug this. Although If I've just made a numpty configuration mistake, let me know.

{"Defaults":{"AbortOnConnectFail":true,"AllowAdmin":false,"BacklogPolicy":{"QueueWhileDisconnected":true,"AbortPendingOnConnectionFailure":false},"CheckCertificateRevocation":true,"ConnectRetry":3,"ConnectTimeout":null,"CommandMap":null,"ConfigurationChannel":"__Booksleeve_MasterChanged","DefaultVersion":"3.0.0","KeepAliveInterval":"00:01:00","Proxy":0,"ReconnectRetryPolicy":null,"ResolveDns":false,"SyncTimeout":"00:00:05","TieBreaker":"__Booksleeve_TieBreak","ConfigCheckInterval":"00:01:00","ClientName":"mqube-auth-service-mqube-auth-service-56fcbb588c-b2nsh(SE.Redis-v2.5.43.42402)"},"AbortOnConnectFail":false,"AllowAdmin":false,"AsyncTimeout":10000,"UseSsl":false,"ChannelPrefix":{"IsNullOrEmpty":true},"CheckCertificateRevocation":true,"ClientName":null,"ConnectRetry":5,"CommandMap":{},"ConfigurationChannel":"__Booksleeve_MasterChanged","ConnectTimeout":10000,"DefaultDatabase":null,"DefaultVersion":"3.0.0","EndPoints":[{"Host":"redis-ha-announce-0","AddressFamily":0,"Port":26379},{"Host":"redis-ha-announce-1","AddressFamily":0,"Port":26379},{"Host":"redis-ha-announce-2","AddressFamily":0,"Port":26379}],"HighPrioritySocketThreads":true,"KeepAlive":60,"User":null,"Password":null,"PreserveAsyncOrder":false,"Proxy":0,"ReconnectRetryPolicy":{},"BacklogPolicy":{"QueueWhileDisconnected":true,"AbortPendingOnConnectionFailure":false},"ResolveDns":false,"ResponseTimeout":0,"ServiceName":"mymaster","SocketManager":null,"Ssl":false,"SslHost":null,"SslProtocols":null,"SyncTimeout":10000,"TieBreaker":"","WriteBuffer":0,"ConfigCheckSeconds":60}
Unhandled exception. StackExchange.Redis.RedisConnectionException: Sentinel: The ConnectionMultiplexer is not a Sentinel connection. Detected as: Standalone

We're using the https://github.com/DandyDeveloper/charts/tree/master/charts/redis-ha helm chart to deploy this.

Start with the supplied EndPoints, ServiceName, and the Redis HA Helm chart configuration, then trace how StackExchange.Redis classifies the connection as Standalone rather than Sentinel. No source file or test is named in the issue. Done means identifying whether the Kubernetes endpoints or Sentinel configuration causes the mismatch and documenting a reproducible correction or clear next diagnostic step.