Piece disappears while dragging

[Bortseb]

I modified the example below to work in a nodeJS context. https://shaack.com/projekte/cm-chessboard/examples/validate-moves.html

Everything works fine, other than one strange thing. When I drag and drop pieces, they disappear while I'm dragging them, but when I drop the move still completes successfully...

Any clues what might be causing this or how to figure this out?

You can test an early example of what I've created here: https://robert.wiki.openlearning.cc/view/about-chess-plugin

and the code that runs it is here: https://github.com/WardCunningham/wiki-plugin-chess/blob/next/src/client/chess.js

Thanks for any help!