Maybe I am totally overlooking something, but during an ARAM game I was silenced during a meph ult (the global one) and I can’t figure out why. I have the game save if anyone wants to look. I have browsed all the talents of the other team and nothing seems to explain it.
P.s. I did win the game 
It could have only been Diablo’s Apocalypse. You might have been nowhere near him but it still caught you on the other side of the map while you while you were focused looking away from your character.
Another possibility is Malfurion’s root talent. You are allowed to freely cast at first but the moment the root ends, sleep effect takes over.
One more thing that is very possible, Li Ming’s knockback ultimate with lvl 20 upgrade. Insane range with big effect radius which could have caught you from the fog of war.
Everything else is impossible to overlook.