Various different things can happen, it would take me quite some time to dig up examples but at least with elevenlabs you don't get the clicks and pops you get like on notebook LM for example. 11labs instability comes in the forms of intonation, pitch, accent, garbled words or even once language. I've only seen it happen in the 3k+ words gen's I've done, usually actually around the 75% point of the narration of whatever I've converted, and on average lasting a couple of seconds top.