Setting up Draytek router and Windows server 2016

I am using a DrayTek router 2670n have a physical server in my office with Windows 2016 installed.

All computers connecting share the same login IDs with the users on the server and we have folders shared setup on the server.

I'm wanting to create a VPN connection using DrayTek smart client to be able to see the folders on the network. When machines are connected locally it works fine. However when we try and connect to VPN sometimes VPN is not connecting and when it does it works.

I suspected something to do with static IPs or permissions but cannot seem to resolve it despite having deleted users and reinstalled them. As well as users we have groups set up on the server, not sure if this is a conflict? I need to get this up and running