database crash during pgbench run

Hi,
I have a very strong machine with 64GB of ram and 19 cpu but it seems that
when I'm running the next benchmark test with pg_bench the database is
crashing :

createdb -U postgres bench
pgbench -i -s 50 -U postgres -d bench
pgbench -U postgres -d bench -c 10 -t 10000

output :

client 8 receiving
FATAL: terminating connection due to administrator command
client 8 sending UPDATE pgbench_accounts SET abalance = abalance + -1542
WHERE aid = 1142155;
client 8 could not send UPDATE pgbench_accounts SET abalance = abalance +
:delta WHERE aid = :aid;
invalid socket: server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
transaction type: <builtin: TPC-B (sort of)>
scaling factor: 50
query mode: simple
number of clients: 10
number of threads: 1
number of transactions per client: 10000
number of transactions actually processed: 89241/100000
latency average = 27.944 ms
tps = 357.864437 (including connections establishing)
tps = 357.871594 (excluding connections establishing)

it crashes after some time and not immediately.

output from logs :

2018-12-10 19:11:12 IST 505 LOG: automatic analyze of table
"bench.public.pgbench_branches" system usage: CPU 0.00s/0.00u sec elapsed
0.01 sec
2018-12-10 19:11:12 IST 505 LOG: automatic analyze of table
"bench.public.pgbench_history" system usage: CPU 0.00s/0.05u sec elapsed
0.10 sec
2018-12-10 19:11:14 IST bench 25045 LOG: duration: 1451.819 ms
statement: UPDATE pgbench_branches SET bbalance = bbalance + -4059 WHERE
bid = 14;
2018-12-10 19:11:40 IST bench 25049 LOG: duration: 1039.710 ms
statement: UPDATE pgbench_tellers SET tbalance = tbalance + 3596 WHERE tid
= 403;
2018-12-10 19:11:56 IST 23647 LOG: received fast shutdown request
2018-12-10 19:11:56 IST 23647 LOG: aborting any active transactions
2018-12-10 19:11:56 IST bench 25051 FATAL: terminating connection due to
administrator command
2018-12-10 19:11:56 IST bench 25049 FATAL: terminating connection due to
administrator command
2018-12-10 19:11:56 IST sadas 27765 FATAL: terminating connection due to
administrator command
2018-12-10 19:11:56 IST bench 25050 FATAL: terminating connection due to
administrator command
2018-12-10 19:11:56 IST 23654 LOG: autovacuum launcher shutting down
2018-12-10 19:11:56 IST sadas 24821 FATAL: terminating connection due
to administrator command
2018-12-10 19:11:56 IST hadr 24814 FATAL: terminating connection due to
administrator command
2018-12-10 19:11:56 IST bench 25047 FATAL: terminating connection due to
administrator command
2018-12-10 19:11:56 IST bench 25048 FATAL: terminating connection due to
administrator command
2018-12-10 19:11:56 IST hadr 24065 FATAL: terminating connection due to
administrator command
2018-12-10 19:11:56 IST postgres 24818 FATAL: terminating connection due
to administrator command
2018-12-10 19:11:56 IST postgres 24819 FATAL: terminating connection due
to administrator command
2018-12-10 19:11:56 IST hadr 24812 FATAL: terminating connection due to
administrator command
2018-12-10 19:11:56 IST postgres 24817 FATAL: terminating connection due
to administrator command
2018-12-10 19:11:56 IST bench 25046 FATAL: terminating connection due to
administrator command
2018-12-10 19:11:56 IST hadr 24813 FATAL: terminating connection due to
administrator command
2018-12-10 19:11:56 IST postgres 24816 FATAL: terminating connection due
to administrator command
2018-12-10 19:11:56 IST 23651 LOG: shutting down
2018-12-10 19:11:56 IST 23651 LOG: checkpoint starting: shutdown
immediate
2018-12-10 19:11:59 IST 23651 LOG: checkpoint complete: wrote 69557
buffers (4.1%); 0 transaction log file(s) added, 0 removed, 0 recycled;
write=2.800 s, sync=0.045 s, total=2.877 s; sync files=23, longest=0.045 s,
average=0.001 s; distance=573364 kB, estimate=573364 kB
2018-12-10 19:11:59 IST 23647 LOG: database system is shut down
2018-12-10 19:12:11 IST 2641 LOG: database system was shut down at
2018-12-10 19:11:59 IST
2018-12-10 19:12:11 IST 2641 LOG: MultiXact member wraparound
protections are now enabled
2018-12-10 19:12:11 IST 2638 LOG: database system is ready to accept
connections
2018-12-10 19:12:11 IST 2645 LOG: autovacuum launcher started
2018-12-10 19:12:17 IST 2692 LOG: automatic vacuum of table
"bench.public.pgbench_tellers": index scans: 0
pages: 0 removed, 13 remain, 0 skipped due to pins, 0 skipped frozen

some conf parameters :
listen_addresses = '*'
maintenance_work_mem = 128MB
work_mem = 53MB
shared_buffers = 13411MB
effective_cache_size = 32278MB
max_wal_size = 1440MB
wal_buffers = 16MB
checkpoint_completion_target = 0.9
standard_conforming_strings = off
max_locks_per_transaction = 5000
max_connections = 1200
checkpoint_timeout = 30min
random_page_cost = 2.0

any idea what can cause it ?