Sorry for the late response, i did try going back about 10 days in nightly (while cleaning and updating) and was still seeing the error pop up, but this should have worked. Still unsure why--I'll chalk it up to user error! Thanks for your help!
I had tried this initially to no avail. I'll chalk it up to user error! most of my projects started on nightly, but were now able to be swapped to stable. For the rest of them, updating the problem deps (or forking and manually removing the stdsimd feature) fixed it for me, though reverting to a prior release of nightly should have worked. Thanks for your help!