Temporary HP is not supposed to stack. It's that way in the TT version.
This does nothing to address my statement that the way it's design highly devalues the Symbiotic Entity ability. Just because something exists a way in the TT does not make it good. Elves and half orcs borrow their OP racials relative to other races from the TT as well, and monks were garbo in the TT, which is why Larian changed them.
We are not in theology class, the rulebook is not a bible to be followed for a PC game, gameplay balance and design comes first.
