Issue is:
It's possible to configure auto-registration option with a Script operation, where select "Current host" in target list.
The script is configured as "Execute on -> Zabbix proxy or server".
Command like "echo {HOST.HOST} >> /tmp/testlog"

In the Script command we try to use macros like {HOST.HOST}, {HOST.IP} as parameters, which we hope to be expanded correctly and passed to shell script itself.

Issue is - imagine a new host is just registered and when zabbix proxy gets this command to be executed a few seconds later, it does not know the Host yet, so the macros will not be expanded correctly and the command will be failed.

This is an edge case, which is still possible to configure. And would be nice to address it someway, to guarantee that such script operation would be successful.

Maybe zabbix server, when registering a new host for a proxy, should force incremental config update to the proxy, before attempting to run the actions?