Teleport bug [GAMEPLAY]

I've had it happen on several occasions now where i go back to base and when i want to tp (and I've made sure its off cooldown of course) the icon for it goes a darker colour as though I can't use it and when i try to use it I get the notification that it can't be used at that time. This seems to happen for no apparent reason and has almost lost me some lanes and games. Is this a bug or is there a specific reason it won't work?