I have heard of that issue with cpanel and there are 2 different possibilities in this scenario.
1. The isp you are using is changing your ip address periodically instead of having a fixed ip. Causing your cpanel session to disconnect. This is referred to as your dhcp lease time and normally would cost you to get a dedicated ip address through the internet service provider you are using.
An alternative solution to this problem would also be getting a VPN.
2. You are trying to log into cpanel from 2 different locations.