Tysm <3Secure Alert always cause by USING VPN.
It because ur current IP (or VPN's IP)is in the hypixel IP ban list. When a hack was banned, the IP he used would go to the ban list. And it seems that hypixel never reset their IP ban list.
A good way to solve this problem is change ur IP. And this might be the only way to solve. Try to restart ur router if u r using dynamic IP or PPPOE. Ask to ur ISP for more if in need.
Chinese people often have this problem so that i know that very clearly xd