Zabbix установлен из быстрого развертывания  Zabbix 4.4 под Ubuntu. Каждый час zabbix-server останавливается. Ошибка из zabbix-server.log

zabbix_server [13444]: ERROR file:variant.c,line:476 Something impossible has just happened.
13444:20191206:140030.529 === Backtrace: ===
13444:20191206:140030.530 13: /usr/sbin/zabbix_server: preprocessing worker #3 started(zbx_backtrace+0x4e) [0x5624ec35abb8]
13444:20191206:140030.530 12: /usr/sbin/zabbix_server: preprocessing worker #3 started(+0x1ecc05) [0x5624ec37fc05]
13444:20191206:140030.530 11: /usr/sbin/zabbix_server: preprocessing worker #3 started(zbx_variant_compare+0xe8) [0x5624ec37fd44]
13444:20191206:140030.530 10: /usr/sbin/zabbix_server: preprocessing worker #3 started(+0xa8d13) [0x5624ec23bd13]
13444:20191206:140030.530 9: /usr/sbin/zabbix_server: preprocessing worker #3 started(zbx_item_preproc+0x301) [0x5624ec23d422]
13444:20191206:140030.530 8: /usr/sbin/zabbix_server: preprocessing worker #3 started(+0xa1afa) [0x5624ec234afa]
13444:20191206:140030.531 7: /usr/sbin/zabbix_server: preprocessing worker #3 started(+0xa1dbb) [0x5624ec234dbb]
13444:20191206:140030.531 6: /usr/sbin/zabbix_server: preprocessing worker #3 started(preprocessing_worker_thread+0x277) [0x5624ec235712]
13444:20191206:140030.531 5: /usr/sbin/zabbix_server: preprocessing worker #3 started(zbx_thread_start+0x37) [0x5624ec368ad9]
13444:20191206:140030.531 4: /usr/sbin/zabbix_server: preprocessing worker #3 started(MAIN_ZABBIX_ENTRY+0xe7a) [0x5624ec1d3f45]
13444:20191206:140030.531 3: /usr/sbin/zabbix_server: preprocessing worker #3 started(daemon_start+0x2f0) [0x5624ec35a327]
13444:20191206:140030.531 2: /usr/sbin/zabbix_server: preprocessing worker #3 started(main+0x305) [0x5624ec1d30b5]
13444:20191206:140030.531 1: /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0) [0x7feb784eb830]
13444:20191206:140030.531 0: /usr/sbin/zabbix_server: preprocessing worker #3 started(_start+0x29) [0x5624ec1d2129]
13362:20191206:140030.533 One child process died (PID:13444,exitcode/signal:1). Exiting ...
zabbix_server [13362]: Error waiting for process with PID 13444: [10] No child processes
13362:20191206:140030.581 syncing history data...
13362:20191206:140030.603 syncing history data... 100.000000%
13362:20191206:140030.603 syncing history data done