Personally, My PPPoE has a dynamic public IP. But as this connection is outgoing then your PrivateIP from your ISP should not be a problem at one point your traffic will go out to the internet from 1 public IP address. so if my assumption is correct then your problem is config, not the private IP. as you successfully connected from windows behind double-NAT.
I would recommend you to check this post. It might help you to find where is the problem. My VPS is an x86 MT.
http://forum.mikrotik.com/t/route-internet-traffic-mt-via-wireguard-tunnel-through-mt-wg-peer/154825/1