My question is very similar to this question:
Except it differs in 3 key ways:
- The solution did not work for me This occurs ONLY on Facebook.com; reddit, twitter, netflix, etc.'s "remember me" function works fine.
- The erasure of the cookies does not occur during restart of the browser. In fact, I can restart safari and still be logged in.
- The erasure happens when I put the computer to sleep and wake it up again.
I have confirmed that the cookies are being reset. The cookie list is entirely different on wake, and I am booted out of Facebook.
The curious thing is that it only occurs for Facebook. This is really annoying though, and my next resort will be a full reinstall.
Newest model Retina MacBook Pro (August 2014) running OS X 10.9.4 Safari 7.0.6
It seems to have been resolved for now, with a "Repair Disk Permissions" from Disk Utility, although I suspect it will occur again.
This is a long time after I asked the question, however I did eventually figure it out. It turns out that I had connected my Skype to my Facebook account, and that was somehow triggering a logout every time I opened Skype (that's why it seemed so random). So solution for anybody who's having this problem: just disconnect Skype and Facebook. Never had this issue again.