Experiment never shows variant page
I have my experiment code on the original page (the home page), and UA code as part of the site-wide template, and both the original and variant have passed validation. I have the test set to run on 100% of visits to the original and split traffic evenly between the 2
When I visit the home page, it adds a utm_expid string to the URL, so something is happening, but it never serves the variant. I've tried across multiple browsers and computers, so it's not a caching problem. Nothing is being recorded in the experiment either, even though my real-time reports show 20-40 people on the homepage at any given time.
Can anyone give me some tips on where to start looking to correct this?