Missing coins..?

For the last couple months some of my coins disappear. I save them until I have enough for like $20 in gift cards. Anyway, it's happened 3 separate times that I was over 10,000 coins than all of a sudden I'm back at like 8000 and having to build my amount back up. It hasn't happened in a couple weeks but I just got over 10,000 again and it reminded me of it. It's always at the 10,000 mark. So I was just curious if anyone else has had anything like this happen to them?