I am not having any problem registering with those settings. Are you saying it is just a re-registering problem after you have lost registration? How often are you losing registration? Can you simulate it without having to wait for the problem?
Here is my concern with your set up. And I think we get into trouble here because CC isn't fully aware of the defects in 3CX.
With the setup you describe, 3CX is pulling the SRV records from callcentric.com and as we know it is defaulting to alpha10. But it is only using the SRV record for server selection not port selection. So registration is happening on alpha10 port 5060 with your set up. I don't know how stable that is or why 3CX loses and can not reconnect under that situation. If CC loses alpha10 you should be able to get back on another server. One question I have is while callcentric can change both servers and ports in SRV records, will they still listen to 5060?