Dear Fu,
Please check with the latest version of Mendix. The data source are only added recently 8.7, there might be some fixes later
https://docs.mendix.com/apidocs-mxsdk/apidocs/property-types-pluggable-widgets#widgets
Also the datasource should point the valid path. So if you moved the property in sub property you can use “../datasource"
Or did you rename the data source?
Cheers, Andries