Pre-3.4 versions have the same issue, but starting with 3.4 it becomes a bit more painful due to hardcoded 1 second task sending period.

Steps to reproduce:

1. Create new proxy in Administration->Proxies
2. Choose Proxy mode: Passive
3. Put non-existing and non-numeric macro in Port
4. See server's log file

Similar result can be achieved if you choose TLS connection to be used with proxy and server does not support it.

Result:
Every second there is a message about failed connection to proxy.
Expected:
Since the root cause of connection failure is misconfiguration there is no chance it can be solved sooner than next reload of configuration cache by server. It makes no sense to continue polling mis-configured passive proxy until then.

Similar woes with invalid item update intervals were faced and solved in ZBXNEXT-1675.