network router config

I have Zyxel EX3300-T0 router, with one static ip adress. Router have 4 ports, two of them is IP TV ports,where is assigned static fixed IP adress, on this adress i have Almalinux server with Plesk on it. Problem is - when i connect to this router from other pc, over cable or wifi, then all websites and plesk panel itself is opening very very slow, but if i connect from any other internet source, like mobile internet, then everything working very fast.
Internet connection is optical 800mb/s up and down. Help me configure router settings.
Please connect over Teamviever to me