SDK7: openNftDialog() often fails to complete filling in the popped up 2D UI

Sometimes it works for an NFT urn.
Other times the same urn does not work.
Seems to be much of the time that it fails

Steps to reproduce:
Create or visit any scene where NFTs have a way of opening their dialog
// example scene: https://gitlab.com/dcl-tech/nft-tests
// existing examples: 5,117, or the Unity cafe at 14,100

Invoke the dialog, it pops up its 2D UI
// expected: you promptly see the image and text appear
// actual: much of the time you get a spinner 'foreever'