Solubility of Amylopectin and Glycogen in water
The answer is relatively simple: Amylopectin is watersoluble, and this seems to be a classical textbook error, which has been propagated now for decades. As you say yourself, the only difference is the number of 1,6-glycosidic branches, which occur every 8-12 glucose monomers in glycogen and every 15-30 monomers in amylopectin.

There are even scientific articles which show that amylopectin is watersoluble, see the references below:


Green et al., Journal of Chemical Education vol 52, p.729 (1975) Which  Starch Fraction  is  Water-soluble,  Amylose  or 
Amylopectin?
J. Robyt, Encyclopedia of Life Sciences (2001) “Polysaccharides: Energy Storage”