I have a Archer C9 v3 with 4 computers connected. Two are wireless and the other two are ethernet. I need them to connect to a server using vpn and I have managed to troubleshoot that I can connect any of them but they cannot all be connected at the same time. So If I connect computer #1 then #2,3,4 will not connect. However, if I connect #2 it will work but then #1, 3 and 4 cannot connect. They are using the Windows 10 built in VPN client using L2TP w/PSK. On the router, I looked under NAT Forwarding > ALG > and everything has a check in the box but specifically the boxes for the following are checked:

• Enable PPTP passthrough 
• Enable L2TP passthrough
• Enable IPsec passthrough

What can I do to allow all four computers to connect to the VPN?