What does the transparent circle around an animal tracker on the compass mean?

Randomly, a transparent circle appears around the tracker icon on the compass for an animal:

I found some speculative Reddit posts about this, but no solid answers/none of the comments seem to hold true for me. I thought it might also mean that the animal is the nearest to me, but that doesn't seem to be the case from testing.

What does this transparent circle mean?

Solution 1:

Apparently, it has nothing to do with quest items, rarity nor proximity. Several users on Reddit say it's just a bug. When new things show up on your compass, they have a circular "ping" that grows and then shrinks back down to nothing, attempting to alert you to their presence. Sometimes they don't go away properly.