I am using a number of different keyboard layouts, depending on which language/keyboard I am woring with. Some of these rely on the AltGr key for producing certain symbols like @ (e.g. the Swedish layout).
Since I updated to Windows 10, the AltGr key intermittently ceases to work (while Ctrl + Alt + still works). Similar issues have been reported with Win 8 and Win 8.1, but the solutions to these do not apply to my case (and perhaps not to other Win 10 cases. So I will try to be very precise in describing the issue here.
To start with, when I say "the AltGr key stops working", what I mean is that it fails to act as Ctrl + Alt (which is what it is supposed to do). However, it does do something: for example, when I press AltGr + 2 and then another ordinary key, say "A" what I get is "2a". Note that the 2 does not appear until I press the "A". In other words, when pressed with AltGr, the "2"-key is somehow treated like a dead key.
Changing between different keyboard layouts does not help. AltGr will not work neither in those other keyboard layouts nor in the original one when I switch back to it. The only way to get AltGr working again seems to be to reboot the system (though I have also seen instances where a reboot from a system with a working AltGr key led to a system with a non-working AltGr key).
It also does not make a difference whether I use the Windows 10 screen keyboard or the hardware keyboard. In the case of the On-screen keyboard, pressing the AltGr key correctly displays the characters on those keys that have one assigned to them (in combination with AltGr), but despite this, tapping one of those keys does not produce the displayed character.