Needs JS and suggest deleting clones or pressing stop before each run so extra clones don't confuse the issue
The label block basically creates a clone and changes its name to a JSON list of the name of the variable supplied and the variables value and then uses my custom text costume block to display it
When the clone is initialised, it sets it name to a random string now
The create label block waits until this has happened before proceeding to create the costume and this guarantees that the clone sprite local variables have been set
You've caught the clone in half-baked state. It seems that some of it's properties (costume) are not ready before yield.
If I launch>tell(clone)... everything goes OK.
Probably a subject for a staff.