Gates Disappearing O2

Maybe I'm an idiot, I don't know, but multiple gates I've leased have disappeared in a new month. I met the leasing costs, had routes going through them (profiting quite a bit of money, might I add), and had them all connected to my network. Suddenly, September 1960 rolls around and the gates are gone! My routes still exist, and they claim I'm still making a profit, but my leased gates are no longer there. They don't show up in research, in the gates menu, under my destinations, in leased gates costs, anywhere. I thought it was just a little bug so I re-leased the gates, but none of the slots are registering as used, and none of the routes are being changed at all. 

I'm seriously confused, and due to some financial troubles during startup, very stressed. 

EDIT: To be specific, the airports with the "phantom games" were Heathrow Intl. and Birmingham Intl.