We've had similar problems, regardless of whether the Chromecast is generation 1 or 2 (have not tried the Ultra). It's a bit hit or miss which is making it weird. ~140 classrooms are now outfitted with Chromecasts. Our high density schools have MR53's, while our lower density schools have MR33's. The schools with MR53's report no issues with the Chromecasts, however we are increasingly (last 1 month or so) getting reports that the Chromecasts attached to MR33's are unable to cast properly. They will display the screen cast, but then when you go to play dynamic content like LucidPress, youtube, WeVideo etc, nothing happens. Rebooting the AP does not make a difference, though we did find that hard wiring the Chromecasts to a VLAN within the same layer 3 segment resolves the problem. I do not suspect it is related to the AP being overwhelmed, nothing indicates that and we get similar results even if I go to the school when no one else is in it. So the problem seems specific to the AP model #, not the Chromecast generation.
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