I'm having this same issue with a couple of my games and for the life of me couldn't understand what it was. It also just said "undefined build" which didn't help at all. But if it's a glitch through the itch.io app, maybe I can just download the game via the website?
Ya I did! It still won't work through the itch io app installer, but I can download the games that wouldn't download from the app, at least from the website instead. Unfortunately, that just means it acts as a separate download. So when I play the game I can't do so from the itchio app launcher. I have to do so from where I downloaded the game to. Which is fine. As long as I can play the game!