MariaDB Galera 3-Node Cluster Sometimes Doesn’t Serves

I have 3 Node MariaDB Galera cluster. I am using "mariabackup" as the wsrep_sst_method, but the database system doesn’t work properly. I can say that sometimes there are 100 connection requests per second from clients, so it is a bit bussy system but sometimes the db system doesnt serves for 2-6 seconds. Connections are lost or the db is unreachable, so when I check in that times the wsrep status is not synched. What should I do to build a 3 Node MariaDB system that can work properly for a bussy connection traffic? There must be something?