Have you tried the 0.5_nat version I pm to you? Does it have the same issues?
I have been running it for 1h30m and so far it has not disconnected. not even once. I'll leave them running and report back later.
edit: added a period to make it clearer.
edit2: it happened again
it took longer, but same effect.
Since you've pointed out that you're getting TCP errors on your network before zm reconnects (TCP Retransmissions in particualar): I'm not dealing with the TCP/IP layer in zm, that's the responsibility of the kernel. It seems that your router/nat has troubles to keep multiple connections open, it just closes them after some time.