they are completely silent for me.

i still hear his voice, but the hits from his axe, the charging, breaking & exploding of his shield, the ultimate scream'ish sounds are all gone

I have exactly the same problem with hextech sion which they believe could be the problem!? please help with this one thanks

I have the same problem...thought it was just me.

I also have encountered this problem.
I think it happens after you activate something (his ult?) the first time, then all of the sounds after that are silent.

From what I've seen, it's from the start of the game, I'ts been happening to not only me, but enemy sions as well. I can't hear their sound effects either
Edit: I was playing on hextech sion, bu tthe other enemy sion was classic. I don't think it's just one

Just posting to say I have no sound for him either, hope devs see it