I recently figured out how to use structure blocks to upload real in game structures from minecraft. I was trying to make an end city ship with the structure blocks and it wasn't generating the loot pools for the chests and wasn't spawning the entities. I then expirimented on other structures. Only pre-1.16 structures had this problem. Bastions and Ruined Portals worked fine with this method. If this is a feature and the functions have been updated, then please let me know.