The problem is that "Distinct Counts" are semi-additive.
The Line Chart applies the calculation for each year, e.g. answers the question for 2018:
In 2018, how many products had a session count greater than 5?
The sum of the Line Chart could potentially be less than the Card if an App had 7 total sessions, but 3 were in 2017 and 4 in 2018 - in that case, the App, which is counted in the Card, would not be counted at all.
In other cases, the sum of the Line Chart could count the same App twice, e.g. it had more than 5 sessions in 2017 and more than 5 in 2018.
In regards to the measure i accepted as a solution - it is working well but i seem to have a problem when i am putting it in a graph. The numbers do not add up - i have included a picture
This is the exact same measures just put in a graph over 3 years. When i filter on the specific years it shows me the number in the graph. But when i add them all together there is a difference from the KPI on top. Do you have any idea why this is?