Windows 11, SkyTemple 1.6.3. I was using Tilequant to convert backgrounds, with the "Reorganize colors only" setting (though I believe it happened with the "No dithering" setting as well.) Closing and re-opening SkyTemple seemed to fix the issue?
These aren't the same files I originally got the error with, but these ones have given the same error. All I did here was update the palettes, using paint.net. (This time's error log has been attached as well.)