mariadb – Thoug max_allow_packet is 1 G , “ERROR 2006 (HY000): MySQL server has gone away” appear

I installed Mariadb 10.5.12-1.el7 on Centos 7.9

Sometimes when I run some query like “SHOW VARIABLES LIKE ‘max_join_size’;” , this message appear :

ERROR 2006 (HY000): MySQL server has gone away
No connection. Trying to reconnect…
Connection id: 3515012
Current database: *** NONE ***

I setup a cluster Packemaker/drbd/mariadb

And these are the conf:

max_allow_packet = 1G 
bind-address = 0.0.0.0
datadir= /db/mysql/
socket=/db/mysql/mysql.sock
log_error=/var/log/mariadb/error.log
skip-external-locking
innodb_buffer_pool_size        = 75G
innodb_log_file_size    = 18G
innodb_buffer_pool_instances    = 75
max_allowed_packet      = 1G
thread_stack            = 256K
thread_cache_size       = 2000
max_connections        = 2000
query_cache_limit       = 256K
table_open_cache        = 2000
table_definition_cache  = 1400
expire_logs_days        = 10
max_binlog_size   = 100M
default_storage_engine = innodb
innodb_file_per_table = 1
interactive_timeout     = 30
wait_timeout    = 30
query_cache_type = 1
query_cache_size = 36M 
query_cache_min_res_unit = 2K

What is the cause of this issue ?

Thanks