I created an error dashboard with a widget that shows our pages with highest average page load time and over how many sessions this value was tracked.But I do not know why Google Analytics shows zero sessions entries - what values are this?
Why are there zero session entries in the highest page load times Google Analytics report?
google analytics
This article on support.google.com explains a similar effect on custom reports:If you build a custom report that has page level dimensions (such as  Page, Page Title, or a page level custom variable, Users may be  greater than Sessions. This may occur when combining Sessions with any  page level dimension because Sessions is incremented on, and  associated with, the first hit of the session.It goes on to show that Session is only counted on the entrance page.So, pages which no user has entered would show zero sessions.