I've been noticing that over the past few weeks, once a user logs into my website, they must hit either Command+R (Mac) or the F5 key on Windows in order to actually be logged in.
For example, users go to http://example.com/wp-admin. They are prompted to type in a username and password (do so successfully) and are redirected into the admin area. From there, when they go to example.com, the content appears as though they are still logged out. If they "hard refresh" the page, everything seems to work again.
I've tried disabling plugins and optimizing the database. Any other ideas? Thanks!