Views gives 200 instead of 404 if incorrect argument and a pager is present I am using with success the global null variable as described here 
How do I set my views to return a 404 using Global: Null under contextual filters?

The solution by Kiam works fine, until a pager is added.

So, 
myviews/mybadarg returns 404, but
myviews/mybadarg?page=2022 returns 200

Any tips why?

I tried enabling and disabling pager but no luck.
I found a solution: I had to set "Show page not found" in the Global Null argument "When the filter value is not in the URL."