Trying to replicate Chuy's Boom Boom Sauce. It's great until it sits then it becomes really thick and has to be microwaved. The restaurant product doesn't thicken after sitting. What could I be doing wrong?

The recipe is peppers, chicken broth (or vegetable) tomatillos, cilantro and cheese. I've tried various cheeses with no success. There's one copycat recipe online that says to use cream of chicken soup but that's not part of the recipe. Granted, I'm a cooking novice but I haven't a clue on why it would thicken so much after sitting a short while. I've bought it from the restaurant and had it sit for days without thickening. Anyone have any ideas? Here's a link to the restaurant version, which I can emulate but not after it sits. I should have taken a pic the last time I made it.http://ift.tt/2sR51gC via /r/food http://ift.tt/2tkTIAY