When we do the pageview retrieval in wikistats we retrieve pageviews for desktop/mobile-web/mobile-app For many wikis (example: https://stats.wikimedia.org/v2/#/sq.wikiquote.org) the pageviews for mobile-app will not exist (a 500 will be returned) but the other two will.
This error breaks the pageview computation from working and pageviews are not displayed.