This happens in 99.9% of cases to users using LTE/3g to connect.

Mobile connections constantly have updates to the IP address of the connection, this in turn means the cookie your machine received after login becomes invalid and this is why you get logged out.

Web-servers like Cpanel/WHM requires log-in into relies on cookies stored on your machine that stores info regarding your IP address and similar info and keeps your session connected securely.

You should consider requesting your ISP/data provider of the mobile connection to give you either:
A static IP on your device
 OR
Extend the lease time on your IP address.