The simulator window being left blank/black is usually caused by Aladin Lite temporarily being down. I’m planning to add backup imagery for when this happens as it’s happening more and more often lately.
Regarding the performance issue, what iOS version are you running?
I haven’t released any update in the past few weeks to the Telescope Simulator so I’m afraid any change in performance must be related to an iOS update. I’ll upgrade my iPad to the latest version and let you know what I find.
As workaround, can you try running Telescopius on a different browser on your devices? I would love to know if you see the same performance issues on Chrome vs. Safari. Thanks!