I skimmed over your routers manual. Some NAT'd routers will not allow UDP broadcasting in this fashion. For a better usage example: in my environment, I have a switch plugged into my router, and all of my connections into the switch. Internal traffic is separated from the router unless needed. If you can, try this scenario. Which in truth, I would recommend even if you are not using HSS. What I would like you to do is setup a 'Special AP' with the protocol UDP, triggers set to port 2564, and incoming the same. Make sure you set this to ENABLED at the top. Now try to send/receive notifications from another computer, using HSS and/or the little app I gave you.
Let me know!
While I work on getting a switch to reconfigure my network, in the meantime I did add the UDP trigger for port 2564 under the Special AP section of my router but yet again it did not change the results. I am truly perplexed what is blocking the broadcast. I also ran Wireshark as Ikon had suggested and while it captured a ton of traffic I didn't see anything in relation to a UDP broadcast on port 2564 from the test app you sent although I am not sure if it shows up as something else on Wireshark or needs some particular filter.
On a separate note I ran Netstat which indicated that your test app is broadcasting on port 2456, so I used that for the router as well however it did not fix the problem either.
Again thanks for everyone's time to help troubleshoot, just not sure why my system is being a pain!