@PeterE no they are not in Redis. They are stored in the state of the core, which you do want to manipulate manually. Maybe someone else can provide a workaround, but you want to be very cautious here.
What I have to say: Why would you use persistent comments in the first place? I never found a good use case for this. Normal comments maybe. But with an acknowledgement you do you want a comment that persists after the acknowledgement perished.
We are looking into the issue at hand regardless.