You may be able to use the developer tools with your browser preview (F12 in most browsers) to get more insight into where things are going wrong. Check the browser console for error messages during or after the experience loads, and that may indicate what you need to fix, or at least point you in the right direction.
To check whether it's your model that is causing the problem, you could duplicate your project, and in the duplicate project remove the model but leave everything else exactly as it is. If everything else suddenly starts working again, then you know it's the model. (Though 60MB doesn't seem big enough to cause problems, I've had projects larger than that that work OK.) If everything else is still wonky after removing the model, then you know it's not the model, but something else that's causing the trouble.
