cPanel error "Your IP address has changed. Please log in again"

When you successfully log in to the cPanel control panel or webmail, a session ID is stored in a cookie on your web browser. As you browse different pages in the control panel or view different messages in your webmail, the session ID will help keep you logged in.

On the server side there are some security checks to make sure the cookie has not been stolen (an XSRF attack) and that your login is valid. One of the security checks is to ensure your IP address remains the same. If your IP address has changed, you will be asked to log in again.

Note: The security settings on our server will permit your IP address to change while its within the same IP block. For example, if your IP address were to change from 1.1.1.1 to 1.1.1.2 this would be acceptable. This is intended to facilitate users connecting from networks like an airport or a university campus, so they won't be logged out if they're moving around.
However, this only applies to IP changes within a /24 IP block (containing 256 IP addresses). For example, if an IP address were to change from 1.1.1.1 to 1.1.2.2 this would not be permitted and you'll be asked to log in again.

When does an IP address change?
This depends on your Internet provider. Some ISPs (Internet Service Providers) will assign a static IP address, so it never changes. Other ISPs will offer a dynamic IP, which could change once a month or once a week, and any time you restart your modem/router.
Most Internet providers, whether business or residential, will assign you the same IP address for a reasonable period of time so that you won't normally notice any issues. The main reason you might encounter this error message "Your IP address has changed. Please log in again" is if you're travelling, for example if you're connecting via a wi-fi hotspot on a train or plane, a hotel or some type of rental wi-fi (like a 4G dongle).

A problem with Three Ireland
Some 4G providers like Three Ireland are notorious for their service constantly switching IP addresses. When you visit a website, you might find different pages of a single web page like images and other content are loaded from multiple different IP addresses.
Thankfully this is not the norm. If you are a Three Ireland customer, you may want to complain that your IP address is changing so frequently that it's impacting the quality of service. You could also ask their customer service team if you can purchase a static IP for your Internet service to prevent the IP address ever changing.

Other solutions
- You could use a different Internet connection
- Make sure cookies are enabled on your web browser
- Complain to your Internet service provider
- Use a VPN (proxy service) like NordVPN