Did you set it up using the push button WPS option?
If so, factory reset the extender and set it up using the installation assistant.
To factory reset, push and hold the reset button for 7-15 seconds while powered on.
Here's a video of how to use the assistant.
also in AP setup: RAXE500->EAX80
1.4gig download/50mbps upload from Xfinity
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