Zabbix not monitoring hosts after database migration

[BerseeM]

Hi,
We migrated to Zabbix 6.0 LTS from zabbix 5.0.
All while also setting everything up on a new VM with a new OS with longer support.

The migration was semi-succesfull. All users, hosts etc were available after the migration but Zabbix seems to do nothing with existing hosts.
The /var/log/zabbix/zabbix_server.log file is also full of this error:

zabbix_server [206725]: ERROR [file and function: <dbconfig.c,DCsync_interfaces>, revision:fdfa8cef9ce, line:2482] Something impossible has just happened. 206725:20230305:083948.550 === Backtrace: === 206725:20230305:083948.550 11: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](zbx_backtrace+0x55) [0x55aab69e669d] 206725:20230305:083948.550 10: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](+0x204e32) [0x55aab6963e32] 206725:20230305:083948.551 9: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](DCsync_configuration+0xfde) [0x55aab696e070] 206725:20230305:083948.551 8: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](dbconfig_thread+0x379) [0x55aab67defb1] 206725:20230305:083948.551 7: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](zbx_thread_start+0x3b) [0x55aab69e99fb] 206725:20230305:083948.551 6: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](+0x6b725) [0x55aab67ca725] 206725:20230305:083948.551 5: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](MAIN_ZABBIX_ENTRY+0x8f4) [0x55aab67cbba1] 206725:20230305:083948.551 4: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](daemon_start+0x3f1) [0x55aab69e61d5] 206725:20230305:083948.551 3: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](main+0x36b) [0x55aab67c9f03] 206725:20230305:083948.551 2: /lib/x86_64-linux-gnu/libc.so.6(+0x29d90) [0x7f407d1e1d90] 206725:20230305:083948.551 1: /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x80) [0x7f407d1e1e40] 206725:20230305:083948.551 0: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](_start+0x25) [0x55aab67c8ae5] zabbix_server [206725]: ERROR [file and function: <dbconfig.c,DCsync_interfaces>, revision:fdfa8cef9ce, line:2482] Something impossible has just happened. 206725:20230305:083948.551 === Backtrace: === 206725:20230305:083948.551 11: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](zbx_backtrace+0x55) [0x55aab69e669d] 206725:20230305:083948.551 10: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](+0x204e32) [0x55aab6963e32] 206725:20230305:083948.551 9: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](DCsync_configuration+0xfde) [0x55aab696e070] 206725:20230305:083948.551 8: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](dbconfig_thread+0x379) [0x55aab67defb1] 206725:20230305:083948.551 7: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](zbx_thread_start+0x3b) [0x55aab69e99fb] 206725:20230305:083948.551 6: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](+0x6b725) [0x55aab67ca725] 206725:20230305:083948.551 5: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](MAIN_ZABBIX_ENTRY+0x8f4) [0x55aab67cbba1] 206725:20230305:083948.551 4: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](daemon_start+0x3f1) [0x55aab69e61d5] 206725:20230305:083948.551 3: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](main+0x36b) [0x55aab67c9f03] 206725:20230305:083948.551 2: /lib/x86_64-linux-gnu/libc.so.6(+0x29d90) [0x7f407d1e1d90] 206725:20230305:083948.551 1: /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x80) [0x7f407d1e1e40] 206725:20230305:083948.552 0: /usr/sbin/zabbix_server: configuration syncer [synced configuration in 0.537621 sec, syncing configuration](_start+0x25) [0x55aab67c8ae5]

This error just keeps repeating over and over again.

When I clone an existing host, the host changes from availablility status unknown to available quite quickly.

[BerseeM]

We decided to not import the old database but to export our hosts and templates via the xml exporter function in Zabbix 5.0.
Everything works fine now.