No idea if this is a recent thing, but I was doing an Operator-only run on Vay Hek and he was disturbingly quiet. No transmissions, no banter, no "WHY ARE THESE FOOLS STILL BREATHING MY AIR?!?!" Nothing. I was devastated.
I thought it might be a settings issue, so I fiddled with the Disable Hint Transmissions and Creator Mode toggles, but it had no effect. Aside from the initial maniacal laughter cutscenes at the start of the mission, nothing. Not a word. On a whim, I switched back to my Warframe and there he went, ranting like normal. Best I can figure, there's a bug preventing him from talking when the Operator is running around.
I haven't done Operator runs on any other bosses recently, so I don't know if it's just Vay Hek who got hit with a restraining order preventing him from talking to star children, but I'll poke some other bosses and find out.
EDIT: It seems like other bosses are also unable to send transmissions to the Operator. I took a run at Tyl Regor and he only spoke when I was using my Warframe.