Why MariaDB cluster always full crash

Hello,

We have a cluster MariaDBCluster (3 nodes) for several years ( about 7 years)
We were facing severals problems during these years
Recently we have again a problem ( we still searching the root cause)

During all these years, each time (99%) the cluster done a full crash ( the 3 nodes in same time not progressivly ) . We never had only a partial crash where the production is not stopped.

What we're doing wrong... What parameters to verify ?

A cluster is still usefull for load balancing / maintenance but not for the high availability....
it's disappointing

Thank you for your help