Try scanning without being connected to your router, just in case the laptop connects with it only at 40 MHz, and therefore ignores the router's actual capabilities.
Otherwise, try a factory default reset.
Went through Administration - Restore/Save/Upload Setting Factory Default / reset
Same thing, both my mac air wifi (built in utility) and my Wifi Scanner app on my mac air, both show 40,not 80. Very weird.
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