So I found an issue in my syslog like the below. I edited the /etc/zabbix/zabbix_server.conf file and changed CacheSize=8M to CacheSize=16M.

Jul 22 20:27:35 knowledge zabbix_server[2778]: Starting Zabbix Server. Zabbix 4.4.10 (revision 4db30afc70).
Jul 22 20:27:35 knowledge zabbix_server[2778]: ****** Enabled features ******
Jul 22 20:27:35 knowledge zabbix_server[2778]: SNMP monitoring:           YES
Jul 22 20:27:35 knowledge zabbix_server[2778]: IPMI monitoring:           YES
Jul 22 20:27:35 knowledge systemd[1]: Started Zabbix Server.
Jul 22 20:27:35 knowledge zabbix_server[2778]: Web monitoring:            YES
Jul 22 20:27:35 knowledge zabbix_server[2778]: VMware monitoring:         YES
Jul 22 20:27:35 knowledge zabbix_server[2778]: SMTP authentication:       YES
Jul 22 20:27:35 knowledge zabbix_server[2778]: ODBC:                      YES
Jul 22 20:27:35 knowledge zabbix_server[2778]: SSH support:               YES
Jul 22 20:27:35 knowledge zabbix_server[2778]: IPv6 support:              YES
Jul 22 20:27:35 knowledge zabbix_server[2778]: TLS support:               YES
Jul 22 20:27:35 knowledge zabbix_server[2778]: ******************************
Jul 22 20:27:35 knowledge zabbix_server[2778]: using configuration file: /etc/zabbix/zabbix_server.conf
Jul 22 20:27:35 knowledge zabbix_server[2778]: current database version (mandatory/optional): 04040000/04040002
Jul 22 20:27:35 knowledge zabbix_server[2778]: required mandatory version: 04040000
Jul 22 20:27:35 knowledge zabbix_server[2778]: server #0 started [main process]
Jul 22 20:27:35 knowledge zabbix_server[2784]: server #1 started [configuration syncer #1]
Jul 22 20:27:35 knowledge zabbix_server[2784]: __mem_malloc: skipped 0 asked 24 skip_min 18446744073709551615 skip_max 0
Jul 22 20:27:35 knowledge zabbix_server[2784]: [file:dbconfig.c,line:94] __zbx_mem_realloc(): out of memory (requested 24 bytes)
Jul 22 20:27:35 knowledge zabbix_server[2784]: [file:dbconfig.c,line:94] __zbx_mem_realloc(): please increase CacheSize configuration parameter
Jul 22 20:27:35 knowledge zabbix_server[2784]: === memory statistics for configuration cache ===
Jul 22 20:27:35 knowledge zabbix_server[2784]: min chunk size: 18446744073709551615 bytes
Jul 22 20:27:35 knowledge zabbix_server[2784]: max chunk size:          0 bytes
Jul 22 20:27:35 knowledge zabbix_server[2784]: memory of total size 8388232 bytes fragmented into 70489 chunks
Jul 22 20:27:35 knowledge zabbix_server[2784]: of those,          0 bytes are in        0 free chunks
Jul 22 20:27:35 knowledge zabbix_server[2784]: of those,    7260424 bytes are in    70489 used chunks
Jul 22 20:27:35 knowledge zabbix_server[2784]: ================================
Jul 22 20:27:35 knowledge zabbix_server[2784]: === Backtrace: ===
Jul 22 20:27:35 knowledge zabbix_server[2784]: 11: /usr/sbin/zabbix_server: configuration syncer [syncing configuration](zbx_backtrace+0x4e) [0x55803bd6662b]
Jul 22 20:27:35 knowledge zabbix_server[2784]: 10: /usr/sbin/zabbix_server: configuration syncer [syncing configuration](__zbx_mem_realloc+0x160) [0x55803bd619af]
Jul 22 20:27:35 knowledge zabbix_server[2784]: 9: /usr/sbin/zabbix_server: configuration syncer [syncing configuration](+0x18c453) [0x55803bd27453]
Jul 22 20:27:35 knowledge zabbix_server[2784]: 8: /usr/sbin/zabbix_server: configuration syncer [syncing configuration](+0x19889b) [0x55803bd3389b]
Jul 22 20:27:35 knowledge zabbix_server[2784]: 7: /usr/sbin/zabbix_server: configuration syncer [syncing configuration](DCsync_configuration+0x12d7) [0x55803bd34de6]
Jul 22 20:27:35 knowledge zabbix_server[2784]: 6: /usr/sbin/zabbix_server: configuration syncer [syncing configuration](dbconfig_thread+0x116) [0x55803bbeb021]
Jul 22 20:27:35 knowledge zabbix_server[2784]: 5: /usr/sbin/zabbix_server: configuration syncer [syncing configuration](zbx_thread_start+0x37) [0x55803bd74862]
Jul 22 20:27:35 knowledge zabbix_server[2784]: 4: /usr/sbin/zabbix_server: configuration syncer [syncing configuration](MAIN_ZABBIX_ENTRY+0x996) [0x55803bbdca4e]
Jul 22 20:27:35 knowledge zabbix_server[2784]: 3: /usr/sbin/zabbix_server: configuration syncer [syncing configuration](daemon_start+0x2ff) [0x55803bd65d8c]
Jul 22 20:27:35 knowledge zabbix_server[2784]: 2: /usr/sbin/zabbix_server: configuration syncer [syncing configuration](main+0x305) [0x55803bbdc0a2]
Jul 22 20:27:35 knowledge zabbix_server[2784]: 1: /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7) [0x7fd8e5ea1b97]
Jul 22 20:27:35 knowledge zabbix_server[2784]: 0: /usr/sbin/zabbix_server: configuration syncer [syncing configuration](_start+0x2a) [0x55803bbdb11a]
Jul 22 20:27:35 knowledge zabbix_server[2778]: One child process died (PID:2784,exitcode/signal:1). Exiting ...
Jul 22 20:27:35 knowledge zabbix_server[2778]: syncing trend data...
Jul 22 20:27:35 knowledge zabbix_server[2778]: syncing trend data done
Jul 22 20:27:35 knowledge zabbix_server[2778]: Zabbix Server stopped. Zabbix 4.4.10 (revision 4db30afc70).