I have a site about weight loss. Right now, I have about 50 articles that are all about various weight loss subjects. On each article page, I have 2 large rectangle ad units, floated right, with the article text wrapping around it. Then up in the top left, I have a banner text-only ad. When i go to my site, and go to one of the aritcle pages, I might see all 3 ad units. Then i reload, and i see one. Reload again, I might see a PSA, and one ad unit. Another reload- perhaps 1 ad unit, the other two are blank. Why is it doing this. The pages have plenty of content; there is an entire article on each one!
It might be because the site is not completely indexed, adsense is aware of it, but had not picked the proper ads yet. On my sites when putting up new pages adsense usually toggles between psa's and somewhat relevant ads and then in a little while start posting extremely well targeted ads. Just be patient