Losing connection on a server

I have an application (via a windows service) running on a service where a client module (.net core) runs Server Events.
However, on 1 specific installation we now get regularly

The remote server returned an error: (403) Invalid User Address.

Any idea why this is happening / in what cases, and how to handle this properly to reconnect?

This validation check can also be disabled with:

Plugins.Add(new ServerEventsFeature {
    ValidateUserAddress = false,

Refer to this thread for context: Issue with SSE and "Access to Subscription 'XYZ' is forbidden"