This issue is related to ZBXNEXT-1022 and ZBX-4284, and is suggestion how they could be solved.

When Zabbix server tries to fetch an item from Zabbix agent, and if the script executes longer than the Timeout parameter, Zabbix agent doesn't return anything and the server thinks there is a network error and because of that can set the host as unreachable. This is bad as it is described in the two issues mentioned above.

Why not change the agent behavior and instead of not returning anything to the server when a script times out, the agent could return a special timed out status to the server for that item and server could report that as an internal event, similar to how not supported works. This way a long running script won't make the whole host unreachable, but only set that item as timed out or some other new state.

Everything else would work like it currently does. If agent doesn't respond to the server, server will think it's a network error and eventually set the host as unreachable.