Why does the Google Optimize experiment increase conversions by 2 times in the base case?

Question

Google Analytics

I launched an experiment with redirects in Google Optimize, I track conversions. For some reason, the conversions of the original version increased by 2 times compared to the average. And on the second option (with a new modal), the conversions are slightly higher than usual on the average for the site. Several times recently on different sites with different experiments with redirects, there was the same situation - the minimum conversion of the base case was 2 times or more higher than the average for this site.
With what it can be connected?