This is a known bug, and one of the ones on the top of the list of things to fix that broke with the latest update.
So here is a temporary tip that will allow you test vision quickly until Control-L is fixed. Create a Dummy Account. Log into that account with a incognito browser window. (using an incognito window will help keep the two game log ins separate). In your GM window, assign control of the token in question to the dummy account player. In the incognito window, the view will immediately reflect the dummy account's vision permissions. In many ways, this is even better than Control-L, because the dummy account will also show you a view that does not show the GM Layer, and where fog of war is opaque, neither of which is necessarily true with Control-L. The dummy account will show you exactly what the player will see.