We have a known issue with Prismic's preview that we can't wrap our head around.
I'm not sure if this is a JS (frontend) or Node (backend) problem (we use Express), but it seems that when a preview token expires (let say I was in preview mode and comeback a week later on our website), the site hangs indefinitely. The solution so far is to ask my team to clear the "Application data" in Chrome, which I think clear the expired preview token.
In the GitHub issue I pasted all the code related to this, let me know if you need anything else on my end.
Here's the error report in Sentry: