I've had a similar problem, though not nearly as frequently as you described. My iPad is unable to connect and I end up rebooting my Nucleus. Looking at the Roon blog and emailing them indicates the issues is likely to do with DNS. Some dynamic ip allocation systems don't seem to play well with the Nucleus. One approach is to assign a static IP. I haven't done this for other reasons and my problem isn't as frequent as yours. Take a look at the Roon blog and/or send them a question. It can be resolved.
Hope that helps,
Guy
Hope that helps,
Guy