My apologies for the delayed response. Thank you for your explanation of the independent and dependent variables of tracking data- I found that very helpful. I believe I was mistaken and meant to say that the data are temporally negatively autocorrelated.
The variograms look pretty normal to me, but I do not know what problems to look for.
I made a github page to demonstrate what I'm seeing. I fitted 4 models- one on the entirety of the dataset, and 3 on annual subsets. Fits 1 and 2 are IID with N>n, and fit 4 is IID with n>N. I thought that in IID data N=n. I had to run the code several times to knit, and one of the times fit4 was actually OUf, which then returned to IID upon the following knit. I hadn't changed the code or data at all, so this has confused me even further.