[BLOCKING LIVE CONTENT] Loading maps to realms often doesn't correctly apply BP and/or RP to those that join

Verification builds: 1.6 Live version

Summary:

When people upload maps to realms from the marketplace, the behavior packs and/or resource packs often don't load correctly and don't get downloaded to players connecting to it.

Impact:

If a map requires the BP or RP and it doesn't load for players, it renders the entire map completely unplayable. This is a major blocking issue for players who want to use these maps on realms with their friends. This issue is exacerbated when large youtubers are making videos on these maps, and things dont work, advertising to possibly hundreds of thousands of people, what a broken game they bought is. This reflects poorly on the Marketplace, poorly on Minecraft and the big one, poorly on creators. They don't know why it broke, they just know on this particular map everything was broken and they are obviously less inclined to buy anything ever again.

Repro Steps:

1. Download a map from the store
2. Upload the map to your realm
3. Connect to it

Observed Results:

There are 3 possible results, all of which occurr when testing multiple times.

1. You will get the BP and RP applied. Great!

1. The BP wont apply, but the RP will, meaning things will look great, but all the behaviors wont work, causing the map to be unplayable.
2. The RP wont apply, but the BP will, so mobs will look right, but they wont act right causing the map to be unplayable.
3. Neither RP or BP will apply, causing the map to be unplayable.

Expected Results:

The BP and RP should ALWAYS be applied. The fact this is unreliable at best is a huge issue, and one that has gone on far too long. People are downloading our maps, and being unable to use them on the service that they are purchasing.

Screenshots/Videos attached:  https://youtu.be/mXJUJBOAirY?t=24m37s Here's a great video of a youtuber with 4.9 million subscribers, connecting to a world hosting Mutant Battle Arena, where the Behavior Pack didn't get applied but the Resource Pack did. It renders most of the mobs vanilla and useless, and removes functionality from the game like the monster vs monster modes. All of the players then think it's bugged and broken, and all 75000 people who have watched it think Jigarbov Productions released a broken piece of content.

Regression Build: Never worked.

Notes:  This has been a known bug for quite some time but it seems noone has ever reported it, probably because replication of the steps is very difficult and inconsistent at best, as the marketplace grows, this issue is getting worse and worse.