The heartbeat is lost to the main MBG. 3 Beats are missed. We see the applications loading because it fails to the secondary site, we can see that in the packet captures. During the whole time the phone is re-transmitting the packet (we cannot figure out why this is happening, is the original issue at hand) the UDP traffic is still solid. So because the TCP stream is broken, the phone doesn't start a new TCP stream to the same MGB but all the while, the 2 devices are talking a-o-k over the network and internet.
I guess what I'm wondering is, even in the case it does fail over in this instance, if the configurations were the same at each datacenter, would the phone drop the call from the original site MGB? It doesn't seem to drop it when the heartbeats aren't reaching, and only does it the instant the phone flips to the second site.
As for the network issue - we appear to have it happen at probably 10 other sites with different internet and router devices. Aruba switches are a constant, all flavours S1500, S2500, S3500.