Hriston
Dungeon Master of Middle-earth (He/him)
(Also - why can't my hand crossbows be on loops of cord, so to reload A I drop B, letting it hang from its cord, and then use my now free hand to help with the reload, and then with a flick of wrist B I bring crossbow B back into my hand?)
I think the issue here is having multiple object interactions that seem to go beyond the simple act of drawing and loading that is included in the attack. If it were that easy you could simply juggle the crossbows, reloading one while the other is in the air.
Seriously though, this is not a "new rule". I'm seeing multiple threads in which the errata are being regarded as rules-changes when in fact they are meant to clarify the existing rules and make the intentions of the designers more obvious. In this case they had forgotten to include language that spelled-out that you need to have a free hand in order to load a weapon, assuming perhaps that this was something everyone would logically understand to be the case. Including that language now should not be understood as changing RAI. I think we can trust the many statements of the design team to the effect that they are only correcting errors and clarifying meanings.