Frequently returns nothing on same query

Hello, I'm using Neo4j on a cluster using the helm chart. but I am experiencing frequent "no result" for the same query that usually returns some nodes and relationships. I want to understand why this happens. is it possible to give me some hints on how this happens, and where I could start to find the source of this behavior? the frequency seems to be exactly 1/5 times it returns no results, while the rest 4 times the same query was sent the right results were returned.

some details: k8s cluster with 3 master nodes and 5 worker nodes 4G memory, 50G storage each, neo4j helm image using neo4j community 4.2.7
where query was sent: python neo4j driver, but also shows the same weird pattern on browser and desktop.