Some (many? all?) Xfinity hotspots have been reported as having their use of the 2.4 GHz wifi band turned off, leaving only the 5 GHz wifi band in operation.
Roku Express/Express+ (not the relatively new Express 4K/4K+ models 3940/3941) and Premiere/Premiere+ (model numbers above 4620) are lower end units with single band Wi-Fi radios that only support the 2.4 GHz band. They, and many other devices of all sorts that are 2.4 GHz only, can't even see the 5 GHz band, let alone connect to it.
I'd suggest you contact Comcast and ask if they can turn 2.4 GHz support back on for that Xfinity Hotspot location.
As an alternate, you could replace that Premiere with any Roku in the current product line (with the exception of the non-4K version of the Express), as they support both 2.4 and 5 GHz wifi bands.
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