Weird problem happening during g71, g70 cycle

I have been trying to run a fairly simple profile on my lathe- a radius and then a straight z axis move. during the the final g71 pass and also the g70 pass, the x axis twitches after going some distance, gouging a bit into the profile, around 0.3 mm into it whereas it should go straight without the x axis moving. I am unable to troubleshoot this problem at all. 

i am posting a link to the video of the problem I am facing, you will be able to see the x axis unwantedly twitch a bit in the last 3-4 seconds if you look closely. any help is much appreciated.

youtube.com/shorts/7KZHbUTbIng

I am running this off a 7i96s. I never changed the servo period, so it should be default. The P value for both axis is 1000

More findings:

I am running g95 with a manual bldc controlled spindle. The jerk happens at around z -17.2 everytime no matter if the spindle was running at 1200 rpm or stopped or at 100 rpm. It never happens before that or after that no matter how much time was given for the axis to reach at that point. So i can safely rule out any problems with electrical noise and such issues (though my control panel isnt good enough).

Now if i change the backlash from 0.08 to 0.0- the problem vanishes.

Even on the graphical interface it looks like a straight like, g70, g71 trie to do a small move at z-17.2 for reasons unknown, for which the backlash motion is triggered. I am not sure yet. Let me increase the backlash to much higher numbers to see if the jerk increases or stays the same as before.

Hi. I see you have the 2.9.3 version. How do you get to work, G71. I have error bad character. Thanks

Thanks for answering. When i run this code from examples its do. G21 G54 G18
F400

O100 SUB
G0 X10 Z0
O101 REPEAT [3]
G1 X[#<_x>-5] Z[#<_Z>+3]
G1 X[#<_x>-5]

O101 ENDREPEAT
O100 ENDSUB

O101 SUB
G72 Q100 X1 Z1 D0.5 I1 R0.3
G70 Q100 X1 Z1 D0.5 P3
O101 ENDSUB

O101 CALL

M2
When from this code i delete G72 line G70 working fine . But when i change G72 to G71 Linuxcnc freezing . Can someone direct me to right path. How to run G71 .
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