changed behavior in JM19:
https://community.jmp.com/t5/JMPer-Cable/New-in-Graph-Builder-for-JMP-19/bc-p/904473/highlight/true#...
It's great that new functions are being added. But, JMP team, please (!!!) keep the old functionality as the default setting!
Otherwise, users will have to change hundreds of scripts!
We wondered about the new behavior:
it always worked. And "today" -- why are the main groups split into small chunks ?

@shannon-c-b , thanks for pointing to the root cause of the "bug":
As a workaround, one can create an auxiliary column to simulate the default (JMP ?-18) functionality of order by () with JMP19:

dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
New Column( "myOrderBy",
Formula( Col Mean( :height, :age ) * 10000000 + :height ),
) << run formuals();
Graph Builder(
Variables(
X( :age, Order By( :myOrderBy, Ascending, Order Statistic( "Mean" ) ) ),
X(
:age_name,
Position( 1 ),
Order By( :myOrderBy, Ascending, Order Statistic( "Mean" ) )
),
Y( :height )
),
Elements( Bar( X( 1 ), X( 2 ), Y ) )
);