Heavy login issues since 4.7.3

I have some heavy login problems.
About 90% of the time I go to my website i'm not logged in.
About 90% of the time I Am logged in, after about 3 clicks i'm not anymore and can't login no matter how much i try with the correct username and password.

This problem occurs since the upgrade to 4.7.3. I haven't changed the cookie-settings in my browser.

A lot of the times the login fails, i see ?time=xxxxxxxxxxxxx in the adresbar.

Please anyone has a solution for this, becouse it's driving me mad!