I’m currently using a GL-MT6000 (Flint 2) on firmware v4.8.2-release3.
After enabling WireGuard (Mullvad), my download speed drops from ~800 Mbps to only 5–10 Mbps.
I am not sure what should I do, I have change other VPN, restart the router, change every connection, it just so slow, when I first set it up the wire-guard, it could go to 580, but when I actually needed to use it it just got no speed. (I have tested lan + wifi)
Hi
This issue seems to be related to server load on Mullvad VPN.
Have you tried connecting to different servers within the same location?
You could also test servers in nearby regions instead of ones located across countries or states, as this often helps improve performance.
Hi Will,
I have tested every server in every VPN I can bought on the market 
, Nord vpn, Cyber ghost, ivpn, mullvad, etc etc, but the issue is after connecting for like 10mins the went from 580 to 10 download mbps, but the upload is like 200mbps.
I asked chat gpt it mentioned that some users reported a WireGuard throughput regression after firmware v4.8.x, and that v4.6.6 or v4.7.x performed much better (500–800 Mbps).
Is this true? If so can you pass me the link I can downgrade back to the version, I am getting really frustrated as I have spent so much money on the VPN and routers 
You can find available firmware here, including historical versions.
GL.iNet download center
We recommend trying the latest beta version 4.8.3 to see if it resolves the issue.
If problems persist, please try to downgrade to 4.7.7.
Here is the installation guide:
Upgrade - GL.iNet Router Docs 4
If the problem persists, it may be related to your ISP or VPN server provider.
As far as we know, some ISPs may throttle UDP rates after a period of operation.
Given that you have a NordVPN subscription, you might try switching to OpenVPN TCP mode to see if the issue persists.
OpenVPN Client - GL.iNet Router Docs 4