In last version the NAT changes are not really works.
i got all few minutes lost connections in and endless loop.
my regulary NAT timeout ist 360 or 600 seconds - that is enough for
a router.
Can you please check your keepalive (tcp based!) coding,
and verify that the miner is working with general settings on natted router ?
Most people are using zm on a natted network I guess, so there should be no general issue.
TCP keepalive is set to 50s in zm so a timeout of 360s isn't an issue.
What OS are you on?
What pool are you using?