Also encountered the same.
Mine was at the Githyanki patrol. Lae'zel had run off as she does so I was controlling Astarion in sneak trying to get him in a nice spot but getting too close triggered the cinematic. The persuasion roll then bugs out as others are finding.
Replicated this at the same spot while controlling Wyll and not in stealth. Doesnt happen 100% of the time but multiple reloads and it happens more than not.
Seems good chance its to do with triggering a PC persuasion roll while in control of a different character?
