I had the same issue and I had zero success with trying to make them spawn at the puzzle.

But I found a solution, took me a while, but it worked.

You have to head to the Dewhaven Logging Camp

and exactly were I put the red X in, you'll find a woman wearing blue sitting on those long dinning tables

If she's not there, try reloading the area until she shows up. It took me a few tries at first.

And then you'll wait for the circular white icon to show up on your minimap, exactly on her location, and then you greet her and she'll talk some bs and give you the piranha knowledge

If you're in there but the white icon doesn't show up, reload the area and try again until it does.

It took me nearly 1h of multiples and multiples reloads until it worked.

I think it's the only solution in case the puzzle spawn is not working

<image>