Issues with KV and NMVB against pre 6.5 cluster

I'm seeing reduced KV throughput and KV operations being retried due to Couchbase.KeyValue.NotMyVBucketException, and being retried. The KV ops never outright fail and are repeatedly retried until the end of the test.

I've run a pass through situational test that does not change the cluster at all during the run, so it's just running continuous upserts against a 4 node cluster with services:
172.23.111.132 - kv,
The rest -
kv,n1ql,index,fts
kv,n1ql,index,fts
kv,n1ql,index,fts

Bucket: 'default' - a Couchbase bucket

Logs

:
http://sdkqe-testresults.couchbase.com.s3.amazonaws.com/SDK-SDK/CB-6.0.5-3340-enterprise/passthrough-KV/06-15-22/053516/30f4d8247705ae1ffbcd4143be763eca-MC.html

This only happens with 6.0 and 5.5, so likely to do with using CCCP, rather than GCCCP (6.5>). 6.0 and 5.5 are technically not fully supported with SDK 3.3 too.