Questions in LCC have 3 parameters in their assets properties:

"assets": [
    0,
    0,
    "1234"
]

With index 1 referencing a media asset (if provided) and index 2 providing a randomized integer. However, the demo json explicitly sets assets[2] to null. This triggers a deprecated function reference error when the qset is run through the score module, causing demo plays to error out and not be submitted.