If your IP address changes between loading the page and requesting the next page or submitting a form, the system will log you out. This is a security measure to protect your account from session hijacking.
Some internet connections (for example, mobile 3G, 4G, or 5G) may change IP addresses more frequently than a fixed-line connection. Likewise some VPN providers may move you dynamically across different IP addresses which will have the same result.
If you maintain the same IP address while using the site, you will remain logged in at all times.