The node doesn't commit query

Hi all.
We use MariaDB-Galera-cluster 10.0.28 with 2 Nodes and one arbitrator.
Last day I saw one of node stuck on all (insert update delete) queries.
After this incident, our node arrived to maximum connection and stuck it.
Another node is working fine and execute all queries and replicating to this node, and doesn't have any warning or error log but this node stuck.
I checked error log and monitoring but I can't find why it happened.
PS: I restarted this node with kill -9 (because I could restart gracefully. Stuck in WSREP: Closing send monitor state) But after a few hours It happened again.
I'm sorry but my English is weak.