This is related to ZBX-26395.
While a workaround was introduced in systemd service file for the specific situation, there are other situations where that won't help. The service can still quietly fail.
A better solution would be to change systemd service type from simple to notify.
But this requires the service itself to notify systemd about successful startup:
https://www.linux.org/docs/man1/systemd-notify.html
https://manpages.org/sd_notify/3

This could be implemented using a wrapper script, but it's best to include it in the agent2 itself.
Possibility of running on non-systemd OS should also be considered, so it should first check if systemd is used.