is multiple publisher configuration a feasible functionality?
Yes you can make as many publishers as your system can handle running.
it was verified that on the servers side the 1st and 3rd publisher
had the same port configuration... which probably triggered this "bug"
What kind of publisher are you talking about? For any but Modbus which have ports, you can use the same port, as it is a client connection to another host at that port. And, in BACnet, it is able to share the local device.
I was able to reproduce the issue. It has to do with the way the old UI stores some state about editing on the server side, and it gets confused when you work with multiple tabs open. To achieve this, you could hit the new publisher button in one tab, then the edit existing in another tab, now go back to the first and save the new publisher (must be the same type or there will be a typecast error), and you've updated the existing publisher! This is not going to be fixed, as the publisher UI will soon be present in the new UI.
why does the following declaration appear?
Ah, so you're using the Mango Persistent TCP Publisher, yes? That message pretty much explains itself. The Receiver is trying to create the incoming point, but it cannot do so because that XID already is being used by another point in the system. You can supply an XID prefix with the publisher such that all points transmitted with have their XIDs prefixed with that string (enabling publishing to localhost). I guess one could manually create a point on a receiver and then add that to a publisher back to that receiver, but I cannot fathom a reason to do so.