Did you spot this post already? It sounds like there are a few people having similar problems…
It occurs to me that if ctrl+alt+F keys don’t work, it may be worth trying ctrl + alt + fn + F key – I do believe that a number of keyboards treat the function keys differently in terms of whether you press the ‘Fn’ to get F-key functions, or if that gives you other things associated with the keys like volume or brightness up/down, media playback controls, etc.