Yeah, that's an issue as old as voice chat itself, I remember that happening all the way back to the mid-2000s. I don't know what exactly goes wrong, but it tends to happen a lot when someone's talking while the game is doing camera cutscenes. It just breaks out of nowhere, as if the origin for the voice data gets overridden at random or something.
#Voice cutting in and out
violet silo
Ironically, there's a workaround for it, which involves using the stopsound command. I'm pretty sure there's a server plugin which stufftext's that command to players either periodically or before/after trigger_camera cutscenes to alleviate that issue.
sterile brook
This is the plugin in question (another w00tguy classic): https://github.com/wootguy/MicFix
Works in 90% of cases from my experience.