Safari 'forgets' cookies, iTunes requires authentication 3 times? I'm having some really odd problems with my new Mac, that I haven't encountered ever before. Every time I restart my iMac, Safari 'forgets' all cookies and stored website data, which means I have to log in to every site again (usernames/passwords are still auto-filled, it's just the cookies, local storage and history which are gone). I'll do that on a regular basis, but daily is a bit too much for me, especially with 2FA activated on most sites.

The second problem which might or might not be related (started about the same time) is that I have to enter my iTunes credentials 3 times in a row before the dialog stops bugging me and I can use iTunes. I don't exactly know what it's doing after the login, it doesn't complain if I hit 'cancel' either.

Talking about a new iMac, OS X 10.10.1

Any ideas?
My bet would be your keychain is corrupt. 

Launch Keychain Access in Applications/Utilities.

From the main Keychain Access menu choose Keychain First Aid.

Enter your password &amp; then Verify.

If it finds any errors, then run Repair.

I've found that after that, it can still find errors to fix, so keep running verify/repair until it runs clean.