I hate to say this, but the tackiness you refer to is a pretty common thing with Vallejo acylics. I wish thier varnishes didn't do this, but they do. I use Vallejo paints almost exclusively but I don't use thier varnishes with the exception of little details that will never be handled. For the rest I prefer clear coats that cure hard like Alclad (both thier solvent-based and acrylic).
I suspect in time the Vallejo varnish will harden, I've never had the patience to wait.
On the second part of your question, I don't have any idea, sorry.
This whole Vallejo tackiness issue baffles me. The paint is popular and widely used, and certainly by gamers painting pieces that will be handled a lot.
I don't know that this is very helpful, but I've shared what I can.