Okay, new router, exact same issue. Going to lose my mind at this point as this worked fine the first time around.
Setup my xxx.asuscomm.com DDNS. Unlike No-IP I don't seem to need to insert a user name and password for it?? Get a registration complete notification on my router's GUI. Not sure if I need to export the free certificate, presumably this is only where I want to use https.
Setup OpenVPN using Randy's guide above, downloaded the OpenVPN Connect file to my phone. Success in connecting to OpenVPN, and it says I'm connected to xxx.asuscomm.com.
Can't connect to anything in ivms-4500. If I select IP Address and insert my xxx.asuscomm.com one, it just says "Connection Failed".
If instead I insert my 192.168.1.xx local address of my NVR. It does the same thing as before, either hangs, or recognizes I have 7 cameras, then I click Live view and it gives me an 8200 error. Clearly nothing to do with the router (so at least I can probably save the $200 I just spent on the 86U given wired speeds are no faster than the r7000 from what I can tell and I use EAP225v2 AP's for wireless).
Seriously, I'm losing it. Just trying to protect my friggin network.
Edit: VPN Subnet mask and subnet, do I need to change these in OpenVPN? VPN Subnet defaults to some 10.8.x.x address while subnet is 255.255.255.0.