My friend has this furnace and he has had these difficulties, but he is still struggling with it. I'll send him your message, I'm sure he'll be happy to.
I had the experience and desire to build my own furnace, but in the end, I had only bad luck, so recently I was disappointed with this idea and I choose the usual built-in furnace, which can be built into the wall and not waste my time.
Have you had any experience in creating stone or clay ovens?