Not saying this is the case but this happened to me once. Though, it didn't persist for 6 weeks! Since the air was dry, i was regularly using a non scented water based lotion on my hands. Knowing in the back of my mind that I should always wash my hands, I still neglected to do so during one day of tank cleaning and water change. The result was the same as you. However, the excessive skimming only happened that one time, I couldn't use the skimmer for some 8 hours. Eventually it stopped.
That said, I've experienced this too with a slight over feeding of phyto and zooplankton that contained amino acids. However, THAT only lasted maybe an hour. Again, other additives can contribute as well. What are you dosing and/or feeding the tank?