Looks like the update to Wunderlist doesn't work on my Lumia 640XL. I assume it will once Windows 10 for mobile is finalized, but it is somewhat annoying I can't get the Windows 8 version and that their site assumes Edge is an Android browser.
Same problem here. I had to do a hard-reset and the app vanished; and can't browse it in the store. So I found a direct link to the app, and it says that "The app isn't available for this device" (L830)
They are actually working on a Windows 10 Universal app for Wunderlist to be official on Windows 10. However, it is currently in Beta and not yet available on Mobile. Hopefully soon.