I'm using 2 domains for my website now for over a year. till recent days, Google was using my preferred domain a.com and seemed not caring b.com. Google didn't penalize me for having 2 domains for 1 website.
Nowadays interesting days I'm having. Google suddenly begun preferring b.com over a.com. I lost some of keywords where a.com was in first page. b.com begun to take over a.com in search results but not as high as a.com.
my sitemap file is on a.com and Google begun deleting a.com URLs of my sitemap.
I'm waiting at the moment how it will result at the end. a kind of experiment for me.
any similar experience?