Issue with FortiClient SSL VPN When Using Domain Name as Gateway

We have two public IPs associated with a single domain name, which we use as the remote gateway in FortiClient. Recently, we replaced one of the public IPs with a new one. Since then, FortiClient VPN has not been working as expected when using the domain name. However, it works when we manually configure both IPs as gateways. What could be the issue, and how can we fix it?
FortiGate