Until about 1 1/2 weeks ago, Google was reporting 6700+ external links to one of my sites. Now it's showing about 680. Have they changed something?
maybe they update their system and found that number to your site. Google is doing a lot of big changes nowadays starting from Google instant and so on...
I wouldn't worry to much, whenever they do certain updates it effects other things. I don't let it bother me.
I have seen these before but it´s google´s way to tell us to keep working on the updates or your ranking will fall down