If your notebook works fine, but the other device is not (on the same SSID, same role etc), this generally suggests an issue with that device's behaviour (if you're sitting in the same place). I'd recommend upgrading the AP92 to the latest code to rule that out, and apply any upgrades to the device relevant to the OS or WiFi bevahiour. If you've already done that, it's likely to be a very low level interopation or RF problem. In which case, troubleshooting on here might become frustrating for you. You're better off logging it with Aruba TAC.
The second question is a very age old one now (how many clients per AP). There is no right or wrong answer from a technical point of view, other than it depends. It depends on the client device application demands, local RF quality, number of concurrent services, backend network configuration amongst other things.
However, the very very simplistic view, is that client count per AP (operating at a "good" level) is somewhere between 15-25. It certainly isn't 2! It can go higher in circumstances (for example) where users are given internet only access of course (perhaps with contracts or traffic management).