My Herschel arrived on the weekend and I made my first test print today.
It is a thin paper and it does buckle after coating, but I didn't find that a problem.
As it is so thin, I can't see how it would be problematic once it's pressed in a frame or vacuum frame?
I have a Nuarc 26-1K and my print came out perfectly sharp.

This paper is beautiful! I think I'm going to get hooked. After years of battling with staining with other papers (even Platine), Herschel comes out with clear high lights and the Dmax is stunning!
This paper is incredibly absorbent! I used 15 drops plus one drop of Everclear (instead of Tween) for an area of about 8 x 4. I also humidify the paper for at least a few hours in my coating area at 60% humidity. I let the paper dry for 30 minutes in that humidity before printing.

I should also point out that I am now doing Argyrotype printing. This paper was recommended for this process.

Perhaps you're drying the paper too long? Or, more likely, your vacuum frame is not strong enough?