Last node in a cluster not responding

Cb 6.0.3
Cluster 2 I/q 3 data
Dataset that can fit into one node of the cluster

Testing with read from replica and also healthcheck using ping we brought down data nodes one by one using stop service.
Assumption - kv will work even when only one Data node is Active as long as read from replica is chosen.

Observation -
The kv queries were working till we only had one data node. And then we didn’t get any response.

What could be the issue?