Internet is super slow with WireGuard VPN ( after upgrade)

Device: GL-SFT1200 Opal
Firmware: 4.3.7 Stable

I used to use an old Nightly or beta version 4.x ( I don’t remember which one exactly ) but when I was using that version my internet using the VPN was really stable with no issues.
But after upgrading to the latest stable. the internet is super slow, a lot of lag …
Speed tests even failing …

I tried to factory reset but no changes. same issue.
Also note that I tested the VPN config using the same access access point, and it works totally fine.
also when I disable the VPN on the router, the speed is totally fine.

I’m connected to VPN server with my personal Friztbox.

Not sure what i can do next.

So the vpn connects but lags?

Can you reset the router firmware and configure again?