Add-on generated structures won’t load entities

Steps to reproduce

1. Import the attached behavior pack.

2. Create a world (infinite, not flat) with experimental features enabled and the attached behavior pack enabled.

3. Find one of the house features in the overworld.

4. /structure load house ~~~

Expected result

Both houses have mobs.

Observed result

Only the house loaded by the /structure command has mobs.

This has been a minor issue for a while now but what happens is I create a structure with entities/mobs within the structure and save the build to a file using a structure block. If I generate the file saved with a regular structure block the build loads normally with the entities still in. However, when I try to load the structure using add-ons (features generation) the build generates normally but entities I saved with the structure are not loaded. This also occurs when I try to load the build with “/structure example ~ ~ ~”. I have tried everything to make it work but I keep getting the same results.

I have attached a .zip file of an add-on that replicates this bug. 

Create a world with this add-on activated and there will be a house that spawns throughout the world. What should happen is that there would be two Vindicators and an Evoker inside, however, this is not the case.