Recently my Windows Server 2012r2 VPN quit accepting connections. I checked the port forwarding, I checked the user logons, I checked the client.All looked fine.
I uninstalled and reinstalled the Remote Access Server Roles along with DirectAccess and VPN (RAS). And it still did not work. After the reinstall, I did have to go back into the settings and remove the modem from RRAS ports so I could still receive landline calls.
Finally, I remembered that I had uPnP turned on for XBox Live but had not had a problem in the last six months or so. But as a test, I turned off uPnP and suddenly the VPN started working. It turns out a new computer recently added to the network was the culprit.
I always believed that the manual port forwarding list would take priority over uPnP but it turns out this is not the case. And it also appears that using uPnP is not the best idea. So after setting up the XBox Live port forwarding, I now leave uPnP off.