I assume you are running a Wireguard client on your Mango, correct? I’ve had similar caps using Mango and AR150, regardless of the ISP connection speed. I don’t know the reason for that, and I have not seen any good explanations. I’ve also seen significant caps running a Wireguard server. I think the advertised VPN speeds are achieved under a different testing setup in a test lab that cannot be matched at home with ISP internet for some reason.