I had this cider in a primary for around 3 months, then moved it to a secondary about 2 months ago. It's been perfectly clear until recently. Over the last couple weeks this has appeared on the top. Anything I should be worried about? Suggestions?
I personally would worry, looks like a pellicle forming. Judging by the pictures, it looks like you have too much headspace in the carboy. It's important to use appropriately sized carboys when bulk storing cider long term, fill them right to the top. Cider films are aerobic, so minimizing air contact is important.
As soon as possible, rack out from under the film (leaving it behind) into a smaller carboy. If you plan to age it more, consider adding 100ppm of sulfites to protect the cider even more. Alternatively, bottle the cider now and pasteurize it to kill off the microbes.
Right- it looks like an infection. There is a HUGE amount of headspace there! You generally want to top up to within an inch of the bung, at the most narrow part of the vessel, to prevent infection and oxidation. The carboy is way too big for the batch size.
Here's an old picture of some of my wines and ciders on a racking day, so you can see the various sized containers and where they are topped up to: