Hey, a squirrel is suspected in a rather fine update in my absence:
True, Roscoe isn’t actually touching the sock in that shot, but he clearly was spending a lot of time climbing on and around it on the morning in question.
A few months ago I had one of these sock feeders fall off the corner of my house where I’d hung it; my investigation in that case showed that the problem was the knot, which had basically untied itself under the weight and jostling of an endless progression of Lesser Goldfinches and House Finches. The CONE SF sock feeder hasn’t had the same level of finch attention, but it wouldn’t surprise me if a single active squirrel could do as much to tug a knot loose as any number of finches.
Elanus' blog here also has great shots of hummingbirds and other birds I hadn't identified.
Looks like the squirrels are getting back in, gotta grease the pole later.