Why minecraft detects I'm using VPN when I'm not?

I was searching for MC servers with PVP, skyblock, etc. When I tried to enter one with VPN/Proxy protection. It said I can't enter while on VPN or proxy, or sometimes it lets me in for a seconds and then kicks me. This only happens with my router, in other places I can join every server, but not when connected to my router. I went to a page that shows you if you're on VPN or proxy and it says "No, you aren't", but minecraft says "Yes, you are"

Servers I tried: PVPLands, MCcentral, and MineHeroes.

It happens with any version, but I only can put those.