I have a Nucleus that I've fortunately never had problems with. Your experience is indeed frustrating, but there have been other posts here like yours but dealing with other brands and types of gear or just communication. In those other cases the problems have been resolved to the customers satisfaction although more slowly than we would like.
It seems many companies are having problems keeping up their normal pace due to problems I'm sure we've all heard about. Roon should provide you with a working Nucleus+. I'd give them a little extra time to do that and notify your credit card company before your recourse time runs out if they don't.