On Nov, 06 I performed following actions:
(1) splited some big general channels into smaller ones according to their placement
(2) set them placement targetable
(3) made Ad Unit - the slot - for each of them (that is unambiguously bound) and
(4) replaced old code (channel-based one) with it

All content and ad formats et cetera stayed the same!
My site looks exactly as it did before

Starting from Nov, 07 my CTR (and ernings) dropped suddenly and it keeps to be low for now.
How could my actions can affect CTR?
CTR depends on the visitors behaviour, doesn't it?!

PS We have several sites of the similar subject, and the only suferrer is the one I reset. So it can't be some global cause...