When you receive "Your IP address has changed" message during login (either cPanel or Webmail), it may indicate one of the 2 possibilities below :
1) Your internet connection is not stable :
if your Internet Service Provider (ISP) has a short DHCP lease time, it normally cause your IP address to be renewed/released and reassigned while you are logged into cPanel.
mobile internet provider (such as Celcom, Digi, Maxis, U-Mobile, etc) are known to have short DHCP lease time, especially if you use hotspot connection.
to avoid this problem, you are advised to switch to a much stable connection, such as Time, Unifi (or, any other fixed-line internet provider).
2) You are attempting to login into cPanel using the same account from two different devices concurrently :
To avoid this problem, make sure that you only login from one device at a time.