I run a forum on which I use AdSense ads. On every page, I have reserved spaces for the ads. Somewhere last year, I noticed AdSense often didn't show any ads in those spaces. Ad income dropped drastically. Then, all by itself, it started an "experiment" where it placed ads wherever it deemed appropriate. It was displaying ads at the weirdest of places, like in the middle of a post. It would actually break a sentence up to display a post wide ad. But on the flip side, ad income increased by almost 400%. Now it's not like I'm getting rich now. We are talking around $10 of ad income each day (with automatic ad placement enabled).

But now there are two problems. The first one being that it doesn't display ads where I tell it to (and that problem is regardless of whether auto placement is On or Off) and that it places ads at the weirdest of places.

So I actually have two questions:

1) What could be the cause of it not displaying ads in the spaces I have reserved for it (which is a problem that started about half a year ago)?
2) How can I tell AdSense to not place ads in certain spots?

Thanks in advance for your help!