Do you have any contents that is shared/accessible from other websites?
e.g. do you have your video players embedded on other websites? Or any social share widgets that has custom link tracking, OR any other such instances?
In such cases you will see those visits/visitors in your report suite, but there will not be an increase in page views (because video views or custom link tracking will not count as page views)
Also check your exit links report for any unexpected domain values. Someone might have copied your source code and pasted it on their website without including the s.t() code section.