I started experiencing an issue whereby a user would try to view a specific product on the front-end which would cause a fatal error. Some users were able to view the product while others were not, this behaviour occured with different products as well. After a little bit of research I mananged to find a similar report of said issue:
Serious bug in Reports module (Magento 1&2) #1018
I can confirm that this is customer/visitor-specific.
I can also confirm that if you are using a full page cache, as soon as a user not experiencing said issue loads the page & primes it into the cache (granted your FPC doesn't hole punch for product view count), the issue no longer persists for the customer who was experiencing it initially, as the function no longer triggers.
