Been noticing this ever since I got my new phone..
When I swipe right to go back to the previous page (or just hit the back button) ns logs me out. Its not a huge deal because ive found that if i just go back to the page i was originally on im logged back in but its still annoying.
Im on an iphone 6s plus with the latest version of ios and i'm using safari. I'm not sure Id have these issues on chrome since I dont use it but yeah its been happening for weeks now.