So I upgraded about 14 hours ago, and have seen consistent connectivity between endpoints! so, if you need a quick fix, upgrade to FreePBX 13.
Note, that my Grub loader, or whatever the OS loader is that comes with the FreePBX distro, had an OS option at top after the upgrade (which asks you to reboot your box) that obviously automatically boots (as it is first on the list), and it kept giving me fatal kernel error. I simply chose the second Grub option, and FreePBX booted just fine, and upgraded as expected. Not sure what the problem is, just letting you all know in case you run into the same issue. I am curious what the new primary option was though, and why it wont boot with it.