This is primarily an autism focused question, although allistics please do chime in if you have something interesting to say!
I’m not referring to stuff like Therians or “not feeling human”, although those are deeply fascinating topics. No I’m strictly referring to finding the task of imagining the human form (in say “daydream stories”) to be unpleasant/uncomfortable.
When I was real young I was REALLY uncomfortable imagining the human form. No problems with animals and weird creatures thought up by toddler me, those didn’t make me uncomfortable!
I brought this up with my IRL friend who’s also autistic. He also experienced something similar!
Anyone else also do this? I kinda want to just… Talk about it. It’s interesting.

I also don’t think I fully understand what you mean, but I have trouble with imagining/visualizing stuff on command. Like the test where you try to visualize a rotating apple in your mind to rate the level of detail you can imagine. Sometimes I can do it fairly easy, other times I can’t for the life of me give it color or make it rotate correctly or even imagine it at all, but it isn’t just being unable to do it when that happens, it’s like my mind just rebels most of the time and imagines everything but the thing I want it to. Other ways that happens is when reading books where it is setting the scene so you can imagine it, but I have a lot of trouble doing it, I usually have an easier time when I’m really hooked, but most of the time it is still hard for me.
Oof. Yeah I don’t have any issues visualizing stuff. I’m no artist so I can’t go into nice details, but I can easily visualize stuff like diagrams, mechanisms, characters doing actions, worlds, etc.
I do, however, struggle fairly hard with describing the orientations/directions/movements of inanimate objects down into words. Part of the issue is “setting the geometric origin”. Eg: “The prongs slide down.” is very context dependent, and I can really struggle with inferred context in literature.
Especially implied subject targets. I’ll be reading something and the next sentence down I’m asking myself “Wait, are we saying all this stuff about person A or person B?”
The brain is a bunch of signal processor and glue logic thrown into a trench coat.