If you try to open a world with a datapack containing a custom enchantment which uses the "structures" sub-predicate, after world load reaches 100% world load stops and you are presented with a "Network Protocol Error" message (as shown in 'Capture2.png'). This occurs for the sub-predicate in both the "entity_properties" and "location_check" predicates.

The issue is definitely with how the game is processing the sub-predicate, and not a syntax error in the datapack, as this error message occurs after seeing the "Worlds using Experimental Settings are not supported" screen, which I believe should only appear if the contents of the pack are valid. To help show this, a file using the "structures" sub-predicate has been attached ('hero.json' Update: changed to the full pack data.zip, which contains 'hero.json').

I should probably also clarify that this is happening when loading a Single-player world despite the error screen redirecting to the server list.

Reproducing the issue

• Add "data.zip" to the datapacks folder of an existing or new  single player world (in the latter case, making sure to enable the pack before clicking 'Create World')
• Attempt to open the world

A video demonstrating what happens, in the case of attempting to create a new world while the datapack is enabled: https://youtu.be/T7TmhgJ9YW8

The error triggers in the same manner for attempting to open an existing world with the datapack enabled.

Expected Results:

After clicking "I know what I am doing" on the "Worlds using Experimental Settings are not supported" screen, the world should load normally and the weapon enchantment "Hero" should increase the players speed when in a village.

Observed Results:

After clicking "I know what I am doing" on the "Worlds using Experimental Settings are not supported" screen, once the world loading screen reaches 100%, you are met with the "Network Protocol Error" screen shown in Capture2.png. You can only select  "Open report Directory" or "Back to Server List" (despite the world being single player). Because of this, the world does not start.