spindle sync trouble - G33.1 Syncronization does not work properly

Hello

my machine:
Mesa 7i76e mit 3 Stepper Motors (xyz)
Mesa 7i77 mit -10 to 10V Servo - A-Axis with encoder
Siemens VFD 15kw with 0-10V on 7i76e spindel-out; direction switch 7i76e over spindir


I have a problem with spindle synchronization for G33.1
Enclosed my Hal file and the ini file.
My spindle has a built-in initiator (24V). It gives 2 pulses per revolution.
I have connected the initiator to an input of the Mesa card.
In the Hal I have set a software encoder and assigned the input of the initiator to phase A.
A second initiator gives the index signal for the start.

I know that two pulses are inaccurate. I will increase the pulses if the spindle needs a bearing change. I will replace the impulse wheel for a new one with more teeth.
Currently the QUICK CHANGE TAPPING CHUCK WITH AXIAL COMPENSATION should compensate the inaccuracy.


#Encoderfunktion laden und mit dem Namen Initiator deklarieren
loadrt encoder names=initiator
addf encoder.update-counters servo-thread
addf encoder.capture-position servo-thread

#Modus des Encoder (Initiator) festlegen 2 Impulse pro Umdrehung
setp initiator.counter-mode true
setp initiator.position-scale 2
setp initiator.x4-mode false

#Eingang Initiatoren
net spindle-phase-a initiator.phase-A <= hm2_7i76e.0.7i76.0.0.input-29-not
net spindle-phase-b initiator.phase-B
net spindle-index initiator.phase-Z <= hm2_7i76e.0.7i76.0.0.input-15

….

#Übergabe position an Spindel planer
net spindle-position initiator.position => spindle.0.revs
net spindle-velocity initiator.velocity => spindle.0.speed-in
net spindle-index-enable initiator.index-enable <=> spindle.0.index-enable


When I execute G-code G33.1 Z-5 K1.75, the machine starts to synchronize the spindle with the Z-axis and moves down to Z-5.
It then also reverses the direction of spindle rotation.
But then the following happens.
Sometimes the machine hangs in G33.1 command and the Z-axis stops. M4 is still active and the cycle must be stopped.
Sometimes the machine moves to Z-5 and then reverses the direction of spindle rotation. Then it moves down further to Z-10. Then stop the G33.1 cycle and it is finished. The spindle stops.
Then I can restart the program. Which of the two scenarios happens seems arbitrary to me.

Does anyone have an idea why this happens?

videos:

drive.google.com/drive/folders/11i6OkLTZ...djmb7Mh8?usp=sharing

G33.1 requires a full encoder (A,B,Z)