Hello,
I had the EXACT same problem with my site (tamworthbaptist.org.au). I generate the navigation dynamically, and I also have a members database that I check to see if someone is logged in, well this was causing this issue particular, fortunately, I was able to create a condition that would only check the member database when it was on the members page (not the WordPress page’s).
This defiantly sounds like a bug, WordPress is not SELECT -ing the database table every time it needed information, but surprisingly, the post excerpt worked, so it obviously is possible to have two database calls on one page, its just WordPress needs to be select the right table all the time.
