Based on some discussions over on another StackExchange forum site over a particular question about user engagement vs. addiction, it was suggested that the question be posed on the Psychology and Neuroscience SE site because it seems to fall into this area of research and is appropriate for the experts in this field to provide an answer.
So the question, phrased slightly differently for this forum:
There have been some recent press about the computer game Fortnite that has caused concern for parents of children that are spending excessive time playing due to its seemingly addictive effect on players (many of whom are young children).
Digital designers working on games often aim to increase engagement using strategies like gamification. Assuming that engagement with an activity involves some similar behaviour to those exhibited in addiction, how are those behaviours measured over time to identify at risk users (e.g. problem gamblers)?
Alternatively, if engagement and addiction are completely different behaviours, what are the differences that allows you to distinguish one group from the other?