I looked into it, and discovered this:
https://lua-api.factorio.com/latest/auxiliary/item-weight.html
An item's weight (which determines how many fit in a rocket) is generated automatically based on the ingredients used to craft it. Then I was thinking about why you wouldn't be able to reproduce the bug and it dawned on me that when you tested it, you were using the default setting of 'Operation Mode' in AAI Loaders for which recipes to use. It has the default recipe (Lubricated) that is cheap, but makes it so the loaders need to be fed lubricant to use. It then has the other recipe (Expensive, no fluid usage) that is more expensive but requires no lubricant to run.
The second setting is the mode I play AAI Loaders in, so with the more ingredients in the expensive recipe, it was causing the weight of the loader to scale outside of rocket range. I tested switching over to the default setting and checked, and indeed those versions of the hyper loaders could fit 5 on a rocket.
TLDR: If you reduce the amount of ingredients for the second recipe a bit, it should be able to be put on a rocket. I -think- simply reducing amount of lubricant to craft it might be enough, but I didn't test any of that.
