Can't help you if you don't want to do as requested since
I will need to dupicate what you are doing asking some simple
questions based on eliminating posibilities to begin with.
G96 is constant surface speed, G46 sets the max speed when in G96,
and G97 turns CSS off ( from my notes / not in the manual, and I
don't use them ).
If you did read the Threading on the Lathe Manual, page 4,
How It Works, then would understand a little why I request using the
generic screen set. There may be problems when using CSS as it may
be fighting the threading which is reading true time rpm value and adjusting the next pass based on the monitored rpm during the threading.
If it does not see the index then the treading cycle won't start. It waites for an index and changes from G94 to G95.
For Now,
RICH