This happens a lot, something on your side whether it is a server or api stops working.
It’s July 5th usa holiday no one at the helm and preview apps are not loading data sources in my data lists. Was working yesterday.
Solution is to setup server alerts when something goes down to notify someone who can start it or a one button action to fix. That’s what we do at our company. Reduced outages across the board.
Happy independence day, thank you for your tool!