I think the problem may just be your IP address changed after the VPN was enabled. Check the IP address of the router and verify if it has changed or not. If it has, then see if you can view your cameras from outside your network by using the new IP address and not the domain name.
Here is some interesting data on your router for VPNs but not completely relevant except for the IP changing. Sounds like a powerful router.
https://www.asus.com/support/faq/114892