What type of bad footage is hardest for ai enhancement to fix?

i have been testing ai enhancement on different clips and i am starting to think the quality of the original footage matters more than the resolution you are trying to reach.

a low resolution clip with good lighting can sometimes upscale surprisingly well, while a higher resolution clip with heavy compression, motion blur or noise can still look terrible after enhancement.

now i am curious about everyone else's experience.

what kind of footage gives you the worst results with ai enhancement?

old recordings, heavily compressed videos, low light footage, animation or fast moving scenes?

also, what do you normally adjust first when the default enhancement produces artifacts?