I am developing a datapack (attached below), and discovered that the salt I had given one of my structure sets was causing the following error: 

Failed to validate datapack
java.util.concurrent.CompletionException: com.google.gson.JsonParseException: Error loading registry data: Value must be non-negative: -1075122312

Through removing and re-adding literally every single file, I narrowed it down to one structure set, (plain_towers, if you want to take a look) and fiddled around with the values, eventually discovering that the problem was the salt number.

The salt was 3219844984, though I have discovered this can be caused by other numbers as well.

Reproduction:

Load 1.19.2

Attempt to load the datapack while creating a new world

Check the game output for the error message