I've been having this same issue since the last maintenance. EVERY time I use the duty finder and placed into an instance I get disconnected. If I have the patience to log back in, I'm lucky to stay on for 5 minutes before it happens again.

I've made no hardware or software changes except for the patch from SE. This machine only runs FFXIV, no anti-virus, no firewall.
I enabled QoS on my router and gave this machine's MAC address the highest priority in case there was some congestion on the network, improbable with only 6 devices but worth a try. This amounted to no improvements.
At this point I'm considering doing some traffic/packet analysis and post up the results in hopes that an engineer at SE could glean a little information from it.