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

What value do you have for P in the ini file, if any?
And what value does the servo period have?
Or is this a parallel port setup?

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

"Bad character" should tell you which line of the G-code the error is on. This is much more likley to be a problem in your G-code than in the G71 code. (not that I exclude that possibility)