1. In version 1.16.210 and above, entities cannot be spawned in the structure, except using the mob spawner.
for lower versions such as 1.16.100 - 1.16.200, entities can still be spawned in the structure.

2. Large Structures load incompletely.

3. When you feel the structures stop spawning, to solve it by deactivating the add-on and reactivating it.