This has happened to me with the Surface 1,3 and 4...........and I just now noticed -for the first time - the virtual 10-key keyboard screen in Windows 10 doesn't have a flippin' comma anywhere. You have to tab back over to the qwerty screen.
There's an exclamation point because....that's useful when you're typing big numbers: $2!435!654.99 but no comma.
Those twits at MS aren't even trying.