They were down?
No, I have been getting my achievements pretty much one at a time the last few months. Everyday one

However the ones that have been reseted were ones I got when I started playing TF2. Like over two years ago.
Mainly the pyro ones. I also lost a bunch of Sniper ones.. So, the time seems to have been unaffected. I also lost a few newer ones for example a demoman one.
I'll email Valve and ask whats going on...