Weird issue - voice chat works in direct calls but not in server channels

So my company is using a Discord server channel for voice meetings in these COVID-19 times, and it works perfectly fine for all of us, except one person. What's very weird is that when I call this person over Discord in a DM, everything works fine. But once he jumps into the channel, he can't hear us and we can't hear him. He's not muted or deafened or anything. Anyone got a clue what's up?