Im having the same problem on my chromebook. If I go to tv.xfinity.com>saved>recordings>program>watch , I get the three dots and the window is non-responsive. If I go tv.xfinity.com>for you>just recorded>program>watch, the recording plays fine.
The issue seems isolated to tv.xfinity.com, as everything works fine on my main x1 box, Roku's, and ios apps.
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