If you have started using the “environments” feature in Google Tag Manager (if not, read why you should at Simo Ahava’s blogpost on environments), then maybe you’ve experienced some weird/confusing behaviour when using the preview/debug functions.
You may have also noticed the gtm_cookies_win=x in your tracking snippet.
After searching for information about the gtm_cookies_win parameter, and not finding anything, I decided to try and debug my way out of it.
Morten Bock 