In the attribute table of the Web AppBuilder for ArcGIS, the numeric field types still show the comma (,) in digits representing thousand when the comma was removed in an ArcGIS Online web map.
In the original data, set the field type as string (text) instead of numeric (for example, zipcodes) before transfering to ArcGIS Online. The web map is not assigned with a comma by default, and there is no comma as well in the Web AppBuilder for ArcGIS attribute table.