New Around Here
Apologies if this is old news to everyone, but on my RT-AX86U running 388.1 Merlin f/w, it turns out that activating the Wireguard VPN server effectively halves/caps download speeds. By coincidence I had also moved to a bigger tier (1.5G) at my ISP and assumed the problem was with them <insert red face here>. After some research I determined that activation of the Wireguard VPN server disables Flow Cache, hence the lower speeds. Deactivation restores speed immediately. With both OpenVPN and IPSec server options (as well as Instant Guard) still available to me on the router, I think I'll just leave Wireguard off!