I maybe totally wrong but what i wonder is if the variable reference “datasource” from fassade row BP used here to set “datasource” from “cast to fassade column” has been set.
If i had to debug it for me, i would try a print string of values in this reference to check if it is ok or not or at least check and set manually variable in blueprint.
Then, if variable seems ok, i would try to set “datasource” in event graph instead of construction script.