That is a good lead I believe.
I’ve reported in the past there is a problem with the Terrain LOD value not being used as percent, but as square root of the value:
LOD Problems - Distances revisited
I unfortunately don’t remember the airport I was measuring this but I believe it was in the “western world” probably around 40N to 45N. I guess someone following the same procedure as I did in the topic but with an airport near the poles, using the dev mode measuring tool, and writing down at which distances the texture LOD changes as you keep moving the drone up, it shall reveal whether the texture LOD ring distances are also affected by latitude and if they are, this could explain a certain number of things indeed.
Your test near the poles seem to be indicating the LOD ring distances are a factor of the grid size, which inevitably changes with latitude, and which makes the whole LOD distance visibility based condition inherently wrong except at LAT 0.