Well, it looks like a Chrome's issue. I've tried to run the code you guys use in different browsers and I see the problem.

navigator.geolocation.getCurrentPosition( e=> { console.log(`latitude= ${e.coords.latitude}\nlongitude= ${e.coords.longitude}`); });

If I run it in the console the Chrome shows me different results, unlike firefox and safari.
I was confused because google maps shows correct location and I was wondering why, so I thought this is Windy's private issue. Then I have looked into the network tab (in google maps) and found there an interesting request - it seems that if your phone is synched with google and uses GPS then they request your location from your phone.
Actually, this issue is reproducable on Windows as well and it's really strange that I was not able to find reported bug on that...