I have heard of people losing C4 control totally when they change their router and thus needing a dealer to “register” the controller on the new network. From the sound of things, you don’t have this issue so resetting all IP addresses to what they were prior to the change may make things.
IF (and that is a big IF - as I am assuming things here, which can be dangerous) the Receiver is IP controlled, you would be able to find the IP address that has been set up in the driver properties in the C4 Composer software.