You should never have to pause your machine to check the blade. The blades dont slip. That's why I wanted you to try a different blade holder to see if that solved the problem of the slippage. You could have a defective holder or blade. Try a different blade and see if solves the problem - then at least we will know it's the blade holder if you are sure that the holder itself is not slipping in the clamp.
As for quality hot press watercolor paper - I am NOT an artist. Let's start there!
I have Studio Fabriano 90 lb watercolor hot press (200 gsm and 25% cotton) that cuts like a dream and feels like a good weight. It is the only hot press that I have. It's not the 140 lb that you have, but I don't have any that weight that is watercolor paper. Is there a reason you need watercolor paper that heavy? I don't know what you are doing so exactly so just wondering if the heavier weight is necessary or if that is just what you had on hand. This machine can handle just about anything but density of any material will change how things cut and some materials do much better with a multicut set up.
We have people cutting chipboard and clay and fondant and sugar sheets and plastics, soft metals and on and on.
Maybe you can get some samples of materials that might work for you and bring them hoe to try out and see what cuts best/ easiest...And maybe you can get something that is not 100% cotton which might make a huge difference. Just throwing out ideas. But first we need to figure out why it seems like the blade is slipping......
EDIT: I talked with Sherri this morning about the watercolor paper and she reiterated that any watercolor paper that is 100% cotton will not cut well because of the density and it takes on moisture as we discussed earlier. And also whenever a company changes their product, no matter what it is, we often have trouble with the new product. When a manufacturer changes, we have seen differences in all sorts of materials from card stock to stencil material and more. So do look for a watercolor paper that had a lower cotton content and see if you can get samples to test cut - and use multi-cut for sure. I hope you can find the quality and cutter friendly material that you are looking for without too much trouble.