Samsung RS21DCNS cool water flow just stopped?

Samsung RS21DCNS popular US-style walk in fridge freezer - everything works, but the cooled water supply stopped.
The icemaker is fine and water is flowing to that. The web/youtube experts all seem to assume it's because the fridge side is not defrosting and the cooled water reservoir held on that side has frozen up - see photo from a YT how-to - but It hasn't - the defrosting seems just fine.

I seem to recall a whirring noise when it was delivering water - but that stopped along with the water a few days ago - andI can find no discussion of this problem. Or any diagrams showing how the water is delivered - pumps, switches etc. Can anyone assist?