We had constantly have had issues with Apple devices, iOS and MacOS. The only thing that kept bringing fixes was upgrading the Ruckus software. You are one a pretty old version. I would strongly recommend upgrading, although version 10 attempts to modernize the web gui and makes everything very big so the interface is harder to navigate, cause it does not fit on the screen.
Mac OS dropping off of the wifi was fixed by trying different combinations of settings having to do with radios and channels.
From what I can see in the NPS log, the MAC and iOS re-login very often, while Windows seems to take advantage of the caching feature. It is possible that during network congestion or NPS high utilisation a few authentications get dropped. But if it happens consistently to the same clients, I would suspect it isn't this.
Last, your NPS server would update its certificate automatically from your AD CA. I would assume that's not a trusted CA, so the user would have to agree to trust the cert in their own devices. I observed this behaviour on my own phone, after the NPS auto-renewed the cert.
But, I would upgrade the ZD, if you can do it and if your APs are still supported.