Backlinks Decreased from 7000 to 4000

X2. **WHAT** are you using to get "200-600" links a week?

It sounds like you're using GSA or automated software. In which case its perfectly normal to lose that many links.

Additionally, you need to consider the following:

1) If you're using ahrefs to check your links, ahrefs is known to be buggy. Especially these last couple months. There's been times where I checked my links one day and they were at 35k, the next day I checked and they were at 300, a few days later they were at 10k, a few weeks later they were back at 35k. So backlink checkers by nature are inconsistent.

2) Blog comments like everyone else said.

3) Links falling off a page like a sidebar widget, sitewide etc.

4) Webmasters deleting your links cause their crap.

Its really not rocket science man. Its either a glitch in the tool you use to check your links, or your links are gone. There is no other explanation. Nobody is stealing your links, your links didn't remove themselves, its as much a mystery as you are informed about the backlinks you're building. And the mere fact that you don't know what's causing it, tells me that you don't actually know anything about the links you're building. Cause if you did, you wouldn't be asking this question in the first place.