It might be if you took out too much of your BB...I think its usually called a mini-cycle since it doesn't take as long on account of still having BB in your tank (substrate, decor etc) and in the canister you didn't touch.
When you cleaned the HOB's did you rinse the media in tap water? Replace the media entirely? I would say with that many filters just clean one at a time and it shouldn't matter if you outright replace everything in it, the other two should be able to keep up with your bio while it regrows. Otherwise, leave your bio in-tact, rinse media with tankwater and replace as little as possible.
Thats my .02, I don't know much though.