The stripping of leading FNC1 characters in GS1 Code128 and DataMatrix codes can be configured through a symbology extension (strip_leading_fnc1). See this article to learn how to set it.
By default, the value is set to true, the SDK strips of the leading FNC1 characters in GS1 Code128 and DataMatrix. You can set it to false if you want to add the missing symbols.
Available since 5.3