280 Ping on Server despite close proximity and sharing network

I'm currently running a 1.19.2 Server with Cisco's Ultimate. My players all have good ping, around 45 on average, while I have over 280. The thing I don't understand is that the Server itself is sitting right next to me, and both my PC and the Server are using the exact same Ethernet connection. Actually, I'm using a single ethernet connection and a splitter to connect both my PC and the Server to the same network. I'm not sure if that's the issue, but does anyone know of something that could be causing this?