LegatusFlagrans

Well, it seems I've isolated my culprit. Of all the things it could be, it just had to be RaceMenu.

I'll try a clean save without removing the shield on back mod mid playthrough and see if I can't replicate it before moving on to isolating problematic mods.

Long story short, I seem to be having spawning issues with the Battle for Whiterun on the Imperial side of the civil war questline. Haven't tested it for Stormcloaks. Basically, once the barricades at the gate are broken, I get these odd clumps of like 4-5 Stormcloak soldiers spawning behind the gates in the exact same spot and becoming stuck to each other and unable to move. They're a pain in the ass to get rid of, too, because they're all still able to attack and you can only hit one at a time unless you fireball them or something. I'm running several mods, but I can't imagine which of them might be the culprit, if any of them. I had removed a shield on back mod prior to the battle in the particular playthrough I saw this in, but I can't imagine doing that would screw the game up that badly, especially since I hadn't experienced any other issues.