I don't know if this mod applies but here goes. In Moonlight Falls, the school lot is really problematic as teen and child Sims do not and cannot go to school when they get there. It seems that Sims cannot enter the building properly and are forced to use other entrances. I have checked other mods and can't find anything related to this. Is the building just glitchy and needs replacing, but what happens if the school building is deleted?

In addition, I'm getting notices that Sims are "unroutable", meaning they're getting stuck in locations, usually at the bookshop. Resetsim seems to work but it keeps happening.

This is the stock combo school/stadium for Moonlight Falls? If I recall correctly, the NRaas developer who put fixes for the combo lots into Overwatch many years ago did not at the time have Supernatural to work with and that one remains problematic. I would recommend replacing it with standalone school and stadium lots.

Replacing the school means that all children and teens will have their School Performance scores reset to 0. If this is important to you, then you might want to record their current performance scores off to the side someplace and set them again using the MasterController command (MC Cheats module required) after they register at and start attending a new school. If you are able to place a new school and stadium before bulldozing the existing one, then adult sims who work at either should have their careers transfer over seamlessly; it's only School Performance for which this trick does not work.

On sims getting stuck elsewhere, by default Overwatch will reset sims it deems to be stuck. This setting prevents us from finding the cause of the problem because by the time we are notified of a route stuck sim, they have already been reset. This combination works out better, because then we can MC > Focus on sims reported stuck (that is, unless the game itself rests them).
NRaas > OW > Settings > Stuck Check > True
NRaas > OW > Settings > Stuck Check Auto-Reset > False

In any event, it is also worth checking the lot for stuck in place jigs (usually invisible objects) that are getting in the way of sims' routing and deleting them. On the lot in question:
MC > Object Stats > Not Inventory (and select anything with "jig" in the name to Flush)

The school building is really quite nice so I don't want to delete it. In the meanttime, a friend has sent me a mod that provides extra doors to schools and uni buildings, so I'll see if that works.
Is this an overwatch, master controller or SP progression feature that works? SP has several push options but none about school, so I doubt that is relevant.

NeutralWarlock post_id=98670 time=1704636958 user_id=25669 wrote: The school building is really quite nice so I don't want to delete it.

Again as I recall, it's nice to look at but doesn't work properly. As in, sims in the Athletic career cannot win any games and thus cannot advance in their careers. Possibly not every player is experiencing this. It's still worth it to check the lot for stuck jig objects, regardless.

I don't understand the last part of your post. It's not that your sims aren't being pushed to school, it's that they are reportedly unable to enter the building. The extra entry mod is great and highly recommended, but still requires the school (or school/stadium) lot to be replaced even if it's with an exact copy of itself or it won't have any effect.

Yes, I having issues with the school in Moonlight Falls which is also a stadium. The problem does not seem to involve athletes going to the building at the same time as students.
I've saved a copy of the school to community lots, so I should delete it and place it again?
I don't think I've ever had any issues with professional sports people not advancing in their careers.

I think the Athletic career issue was just an example of the one of many ways that combo rabbithole can be unusably broken, not related to what it happens to be doing in your game right now.

I don't have Supernatural installed right now to test it myself, but it's technically the combo rabbithole script that has issues and not something about the building itself that is broken yes?
Theoretically, if you'd like to keep the building you could use the Transmogrifer to give the school the script for only being a school.
Which is Sims3.Gameplay.Objects.RabbitHoles.SchoolRabbitHole for reference. MC > Reset Lot afterwards, for good measure.
Then you could either place a new stadium lot or put a CC rabbithole rug near the school to maintain the illusion that it's doing both.

If they still get stuck after that + the additional entry mod, that at least narrows it down to more of a routing issue on that lot.

Overwatch fixes all outstanding issues with combo's that I'm aware of, regardless of which one they are. This sounds like a routing issue. I'd just try saving and replacing the lot to see if it helps.