This what I would expect to see with no ports forwarded.
And this with a web server listening on port 80
I realised exactly what you were saying about the Swann being replaced by the Dahua but was just going through the way the Swann setup works thinking that a similar approach was necessary with the Dahua.
Possibly silly questions, but I agree about the "stealth" response showing the router is at least doing something..
Did you set the default gateway (and correctly) when you were configuring the static IP? It could be the DVR is unable to respond because it doesnt know where to route particularly if the address had changed. Those lack of responses would look like dropped packets.
2 - is the DVR in the correct subnet? Not sure it would let you save if it wasn't, but similar symptoms
Sorry if completely unhelpful