Xiaomi Mi Router 3G slow wired internet speed

I recently experienced slow running OpenWRT on my router (Xiaomi Mi Router 3G). I have a connection of 300 Mbps, while the max I get on the cable is around 80 Mbps. I installed a clean latest version - 22.03.5, and nothing has changed. I turned off ipv6, wifi and no difference. Turning on the "Software flow offloading" option also did not help. After connecting directly to the router from the provider, the problem does not occur. Please help me what else I can try to set.

Wrong or bad patchcord? Just guessing...
See Need some help diagnosing slow wired performance - #3 by mk24