Is that AABB very large, or many entities inside that AABB?
If so it’s a Sponge configuration problem.
As an optimization (that really needs to be disabled by default) Sponge limits the amount of entities checked with getEntitiesWithinAABB for performance reasons (before Mojang added the mob cramming game rule)
Under Entity Collisions
max-entities-within-aabb integer 8 Max amount of entities any given entity or block can collide with. Set to 0 to disable.
Should be set to 0 to disable.
Also if it’s a very large bounding box:
max-bounding-box-size integer 1000
should also be changed.
Sorry for the inconvenience.