Node crashes with Error: Attempt to match against an empty key

I'm using 2 Loadbalancers and 3 MariaDB Nodes as a Galera Cluster.

Only my 3rd Node makes backups every night and a few hours (or rarely direct) after the backup is finished, the Node crached with the following message in the error.log:

2022-09-07 1:18:36 154740 [ERROR] WSREP: Certification exception: Attempt to match against an empty key (0,1): 22 (Invalid argument)
at /wrkdirs/usr/ports/databases/galera26/work/galera-release_26.4.11/galera/src/key_set.cpp:throw_match_empty_key():194
2022-09-07 1:18:36 154740 [Note] WSREP: ReplicatorSMM::abort()
2022-09-07 1:18:36 154740 [Note] WSREP: Closing send monitor...
2022-09-07 1:18:36 154740 [Note] WSREP: Closed send monitor.
2022-09-07 1:18:36 154740 [Note] WSREP: gcomm: terminating thread
2022-09-07 1:18:36 154740 [Note] WSREP: gcomm: joining thread
2022-09-07 1:18:36 154740 [Note] WSREP: gcomm: closing backend
2022-09-07 1:18:36 154740 [Note] WSREP: view(view_id(NON_PRIM,3284c172-ab8d,9) memb

joined {
} left {
} partitioned

)
2022-09-07 1:18:36 154740 [Note] WSREP: PC protocol downgrade 1 -> 0
2022-09-07 1:18:36 154740 [Note] WSREP: view((empty))
2022-09-07 1:18:36 154740 [Note] WSREP: gcomm: closed
2022-09-07 1:18:36 0 [Note] WSREP: New COMPONENT: primary = no, bootstrap = no, my_idx = 0, memb_num = 1
2022-09-07 1:18:36 0 [Note] WSREP: Flow-control interval: [16, 16]
2022-09-07 1:18:36 0 [Note] WSREP: Received NON-PRIMARY.
2022-09-07 1:18:36 0 [Note] WSREP: Shifting DONOR/DESYNCED -> OPEN (TO: 39667715)
2022-09-07 1:18:36 0 [Note] WSREP: New SELF-LEAVE.
2022-09-07 1:18:36 0 [Note] WSREP: Flow-control interval: [0, 0]
2022-09-07 1:18:36 0 [Note] WSREP: Received SELF-LEAVE. Closing connection.
2022-09-07 1:18:36 0 [Note] WSREP: Shifting OPEN -> CLOSED (TO: 39667715)
2022-09-07 1:18:36 0 [Note] WSREP: RECV thread exiting 0: No error: 0
2022-09-07 1:18:36 154740 [Note] WSREP: recv_thread() joined.
2022-09-07 1:18:36 154740 [Note] WSREP: Closing replication queue.
2022-09-07 1:18:36 154740 [Note] WSREP: Closing slave action queue.
2022-09-07 1:18:36 154740 [Note] WSREP: mariadbd: Terminated.

I use mysqldump for the backup script and to make it consistent
it starts with
mysql ... -e "SET GLOBAL wsrep_desync = ON;flush tables;flush logs;"
and ends with:
mysql ... -e "SET GLOBAL wsrep_desync = OFF;"

The certificate and key files should be okay. After I started the MySQL-Server everything is fine. The node is synced from the others. I'm not sure if it really has anything to do with the backup.