WSREP_CLUSTER_SIZE at 0 after rolling update a node

Hello,

I'm currently doing a rolling upgrade of my cluster mariadb galera from 10.3.17 to 10.4.7
I upgraded just a node following instructions.
All seem working fine (the last commit is the same etc... ) The WSREP_CLUSTER_SIZE is 3 on my 2 nodes in 10.3.17 but the WSREP_CLUSTER_SIZE is 0 on my node in 10.4.7 .

i have this warning in log but don"t know if it's linked to my problem .
" WSREP: View recovered from stable storage was empty. If the server is doing rolling upgrade from previous version which does not support storing view info into stable storage, this is ok. Otherwise this may be a sign of malfunction. "

I'm little afraid to continu rolling upgrade another node ...

Thanks by advance