We got strange error on our MongoDB cluster. It consists of 4 replicas with 3 nodes each.
Today, during half an hour nodes from 3 replicas began to crash in chain. Primary crashes -> one of secondaries becames primary -> in 2 minutes it crashes too -> new node goes primary -> again crashes in some minutes and so on. Nodes have autorestart, and in 10-15 minutes of chaining crashes all is ok and works normal. To mention, balancer was disabled at that time.
I've attached two parts of logs with assertion from 2 nodes of one replica. If you need more logs or info - just ask.

We use ubuntu 16.04 on servers and docker containers for mongo.
MongoDB version is 3.6.3