I think I have the same problem. I added the code for adsense as plugin and as html, on both of them it only displays a blank box, or a pink box or a green box, but no advertisement appears. Any help will be apreciated.
Are you sure that the ads to be displayed for your site is approved? Also, can you once try checking the same switching to WordPress default theme like TwentySeventeen and check if the ads will display or not?