Primary node of MariaDB 10.1 got signal 11 suddenly

There is a MariaDB 10.1 Galera environment, which have three node.
We use it as Single Primary Node, say update queries are issued to only node1.

In this cluster, Node1 goes down suddenly with signal 11.
It have already occurred several times, the time and queries are various (= not static).

And it seems that server resource (MEMORY, DISK, CPU) are afford,
and application workload is also not high.