I'm seeing the same behavior as you. It looks like axis tables don't like multiple variables on the X axis. As a workaround, you can stack the variables you want axis tables for, then it will work as you're intending. Script to do this is below.

dt = Open( "$SAMPLE_DATA/Semiconductor Capability.jmp" );
/*dt << Graph Builder(
Size( 834, 588 ),
Show Control Panel( 0 ),
Variables(
X( :PNP2, Combine( "Parallel Merged" ) ),
X( :NPN1, Position( 1 ), Combine( "Parallel Merged" ) ),
X( :PNP1, Position( 1 ), Combine( "Parallel Merged" ) ),
X( :PNP2, Position( 1 ), Combine( "Parallel Merged" ) ),
X( :NPN2, Position( 1 ), Combine( "Parallel Merged" ) ),
X( :PNP3, Position( 1 ), Combine( "Parallel Merged" ) )
),
Elements(
Histogram( X( 1 ), X( 5 ), X( 2 ), X( 3 ), X( 6 ), Legend( 6 ) ),
Caption Box(
X( 1 ),
X( 2 ),
X( 3 ),
X( 4 ),
X( 5 ),
X( 6 ),
Legend( 7 ),
Summary Statistic( "Mean" ),
Location( "Axis Table" )
)
),
SendToReport(
Dispatch( {}, "", ScaleBox,
{Min( -262.805650205971 ), Max( 1221.55660377358 ), Inc( 200 ),
Minor Ticks( 3 )}
)
)
);*/
dt2 = dt << Stack(
columns( :PNP2, :NPN2, :NPN1, :PNP1, :PNP3 ),
Drop All Other Columns( 1 ),
Output Table( "Stack of Semiconductor Capability (PNP2 etc.)" )
);
dt2 << Graph Builder(
Size( 658, 558 ),
Show Control Panel( 0 ),
Variables( X( :Label ), Y( :Data ) ),
Elements(
Histogram( X, Y, Legend( 4 ) ),
Caption Box(
X,
Y,
Legend( 5 ),
Summary Statistic( "Mean" ),
Summary Statistic 2( "Std Dev" ),
Location( "Axis Table" )
)
),
SendToReport(
Dispatch( {}, "Data", ScaleBox,
{Min( 76.197 ), Max( 758.697 ), Inc( 200 ), Minor Ticks( 3 )}
),
Dispatch( {}, "Graph Builder", FrameBox,
{DispatchSeg(
Hist Seg( "Histogram (NPN1)" ),
Bin Span( 3, 0, 4.16666666666667 )
), DispatchSeg(
Hist Seg( "Histogram (NPN2)" ),
Bin Span( 3, 0, 4.16666666666667 )
), DispatchSeg(
Hist Seg( "Histogram (PNP1)" ),
Bin Span( 3, 0, 4.16666666666667 )
), DispatchSeg(
Hist Seg( "Histogram (PNP2)" ),
Bin Span( 3, 0, 4.16666666666667 )
), DispatchSeg(
Hist Seg( "Histogram (PNP3)" ),
Bin Span( 3, 0, 4.16666666666667 )
)}
)
)
);