I have exactly the same problem. The videos that were previously monetized are still monetized. However, yesterday I applied for monetization on my videos and nothing happened and it just went back to the not monetized button. This morning I logged on and all of these videos that just went back to the not monetized button, the button has now gone. Whenever I now apply for my videos to be monetized they are under review for about 30 seconds and then the button disspears? Help! Really need to get this solved soon! My only source of income is through adsense!