Segfault in multiple shard primaries under regular load

Our database is divided into 4 shards, each having one primary, secondary and arbiter. Primaries are r4.2xlarge servers on AWS EC2, and secondaries are r4.xlarge.

Our work load is intensive in both reads and writes, but these servers usually handle the load without a problem. However during their regular work, primaries of 3 of the 4 shards suddenly crashed, within a very short time of each other. We don't know what could have caused this.

Attached are the logs of the segfaults from the primary servers. The one from shard1 seems different that the other two.