Hey there, I've got a gif showing what they mean.
It doesn't matter if they have CC or mods, as it affects both aliens in an unmodded or modded game from what I've tested out. Aliens were fine until some patches ago, where they started to age up to look like generic rng aliens instead of growing up with the features they're supposed to have.
Eyes would enlarge, slightly drifting to the sides, the nose will shrink, and the chins will become pointy. (I also attached some screenshots of an alien I took into CAS with exaggerated features to show how she looks like aging from Young Adult to Adult.)
I feel like this similar to the bug that affected male sims in October 2014 where they had the "wide jaw" glitch, however, this glitch only affects aliens that seem to have bigger noses and smaller eyes that were moved closer, farther, up or down, and chins that were more square to become sharp.
I also think this isn't reported as often since most simmers aren't really playing with their own aliens (non townie spawned aliens)... Or "pure" aliens, as this aging glitch doesn't happen to half aliens.