It happened last year but I still wonder to this day. I was looking for coupons for the site Alltrails. I had a free account and wanted to get a Pro account. I randomly opened lots of search results, but I couldn't find a coupon. Upon going back to Alltrails I was surprised to see I was logged in as a different user (some random dude's account) and it was a Pro account. I was happy about it and downloaded the trails I needed then discontinued the use, and left it unchanged.
What could have been going on behind the scenes, how is this even possible?
This also happened another time on a vastly different lesser-known local site. All of a sudden I see myself logged in as someone else (that I don't know).
Are the sessions / their cookies getting messed up? What are the chances...