Matt Mayberry, who works at a California startup called Dopamine Labs, says it's common knowledge in the industry that Instagram exploits this craving by strategically withholding "likes" from certain users. If the photo-sharing app decides you need to use the service more often, it'll show only a fraction of the likes you've received on a given post at first, hoping you'll be disappointed with your haul and check back again in a minute or two. "They're tying in to your greatest insecurities," Mr. Mayberry said.
On Twitter, the Chief Technology Officer of Instagram, Mike Krieger said that "replication lag/etc. may mean things aren't instantaneous but not intentionally so. and notifications we try and strike a balance of being timely + not over-sending notifs."
I know this may be a "he-said, she said" type situation, but is there any more substantial evidence out there proving one way or the other?