Roku players only work on specific 5 GHz channels. Channel 149 is the most common to use. Why it's not seeing your 2.4 GHz connection (I'm making an assumption you have both) is puzzling, however. But it sounds like your router might have changed channels, which they can do if you leave it set to Auto. I can't say why the older Roku connects, either.
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I realize everything else is connecting to your wireless fine, but I still suggest powering off the Roku, then rebooting your wireless, then trying the Premiere+ again after everything comes back up.
Dan
Roku Stick (3600), Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.