Failover: Server responding with unknown status code for few mutations

+---------+-------------------+----------+--------+

| Bucket  | Type / Storage    | Replicas | Items  +

+---------+-------------------+----------+--------+

| bucket1 | couchbase / magma | 3        | 30000  |

| bucket2 | ephemeral / -     | 3        | 30000  |

| default | couchbase / magma | 3        | 500000 |

+---------+-------------------+----------+--------+

u'test_collections-731': {'error': 'com.couchbase.client.core.error.CouchbaseException | RemoveRequest failed with unexpected status code UNKNOWN {"completed":true,"coreId":"0x6cc277ce0000001a","idempotent":false,"lastChannelId":"6CC277CE0000001A/000000001A4111DC","lastDispatchedFrom":"172.23.106.205:48408","lastDispatchedTo":"172.23.108.70:11210","requestId":602081,"requestType":"RemoveRequest","retried":0,"serverDuration":3,"service":{"bucket":"default","collection":"collection-46","documentId":"test_collections-731","errorCode":{"description":"Command can\'t be executed in a config-only bucket","name":"ECONFIG_ONLY"},"opaque":"0x98eb4","scope":"scope-1","type":"kv","vbucket":773},"status":"UNKNOWN","timeoutMs":120000,"timings":{"dispatchMicros":884,"totalDispatchMicros":884,"totalServerMicros":0,"totalMicros":1377,"serverMicros":0}}', 'cas': 0, 'value': {}}

Request:

Frame: 1772508

Col: 0x3e

key: test_collections-731

Opaque: 0x66240a00

Dest server: 172.23.108.70

Response:

Frame: 1772547

Opaque: 0x66240a00

./guides/gradlew --refresh-dependencies testrunner -P jython=/opt/jython/bin/jython -P 'args=-i node.ini -p get-cbcollect-info=False,skip_cluster_reset=True,skip_collections_cleanup=True,use_https=False -t bucket_collections.collections_rebalance.CollectionsRebalance.test_data_load_collections_with_hard_failover_rebalance_out,data_load_stage=before,nodes_failover=2,rebalance_moves_per_node=32,nodes_init=5,bucket_spec=multi_bucket.buckets_for_rebalance_tests,scrape_interval=5,infra_log_level=debug,log_level=debug,batch_size=20'