Pgbouncer discard all

Hello,
we are running pgbouncer 1.9.1 connected to postgres 10.5

Sometimes we are seeing a lot of waiting connections with this query :

DISCARD ALL

This is our pgbouncer config :

[databases]
dev = host=10.10.10.1 port=5432 dbname=dev auth_user=pgbouncer pool_size=120

[pgbouncer]
listen_port = 6543
listen_addr = *
auth_type = md5
auth_file = /etc/pgbouncer/users.txt
auth_query = select uname,phash from user_lookup($1)
logfile = /var/log/pgbouncer.log
pidfile = /home/postgres/pgbouncer.pid
admin_users = admin
user = postgres
max_db_connections = 220
log_connections = 0
log_disconnections = 0

Do you think this can depend on the server_idle_timeout default config
value?

Thanks a lot,
Nicola