Lan to Lan VPN can't access HikVision Virtual Host URLs

I have a working Lan to Lan VPN (IPsec Tunnel using IKEv2) between two DrayTek routers: 

Local Site
Vigor2926 3.9.9.12
192.168.1.X

Remote Site
Vigor2865Lac 4.5.3.2_BT
172.18.0.X

I have a HikVision NVR at the remote site which has 2 cameras connected directly to the NVR. The NVR has a "Virtual Host" toggle that allows access to cameras connected directly to the NVR using a url with the NVR IP address and ports from 65001 and upwards such as: http://172.18.0.10:65001/
These virtual host URL's do not work over the Lan to Lan VPN, the URL just times out.

Can anyone suggest why this is not working and how to fix? 

From the local site I CAN access the following things no problem over the VPN:
DrayTek web interface on 172.18.0.254
HikVision NVR system on 172.18.0.10 port 8000
HikVision NVR web interface on 172.18.0.10
HikVision Camera (connected to DrayTek) web interface on 172.18.0.11

I can also configure a NAT rule to open port 65001 and connect to the Virtual Host cameras using:
http://remote_site_public_ip:65001
Which of course is outside of the VPN. So I know that the Virtual Host web interfaces DO work. Just not over the VPN.

Hi Simon
For testing purposes, if you use a SmartVPN client instead of LAN to LAN, does it work?
Your remote device would be assigned a virtual LAN IP from the 172.18.0.x range. Perhaps HikVIsion NVR has some limitations when responding to traffic from outside it's LAN?
A different test would be from a second LAN configured on the NVR site. Router supports interLAN routering. Would NVR respond to requests from the second LAN?

I have now solved this, it wasn't any problem with the DrayTek Lan to Lan:

On the HikVision NVR network settings you can configure a Internal NIC IPv4 Address. This is the address the internal PoE ports use. For some reason on this NVR it was set to 192.168.1.254 and the range of the local site network is 192.168.1.X so once the Lan to Lan VPN is established the NVR PoE ports at the remote site were clashing with the network at the local site.

I think the default HikVision setting for Internal NIC IPv4 Address is 192.168.254.1 so I set it to that and now all is working as expected.