I'd chalk some of it up to VOIP being inherently more complex & less stable than old analog phone systems, and the rest most likely due to the agent messing wit

I'd chalk some of it up to VOIP being inherently more complex & less stable than old analog phone systems, and the rest most likely due to the agent messing with their mute button. When I worked in call centers, a lot of us would toggle that mute very frequently while conversing with co-workers. Sometimes to help each other out, but mostly to complain about or make fun of callers. Quite a bit of jaded cynicism in that scene.