I'm using a session custom dimension to distinguish between two variants of my site. I'm setting this dimension to 'A' or 'B' for ALL visits before I track the first pageview.
My problem is that when I look at the number of pageviews in the report I see a much higher number than when I add my custom dimension as a secondary dimension and sum all of the pageviews.
for example, when I count all the pageviews for a certain day I get 100, but if I add a custom dimension as a secondary dimension I see that for 'A' I get 30 pageviews and for 'B' I get 30; overall 30 + 30 = 60. Where are the missing 40?
I assume that somehow the custom dimension is not properly set, but I can't tell why.