Burn shifting right in the middle of a burn

It appears to do it at exactly the same time in any burn.
I am using a Cohesion3D board that runs smoothieware in a K40 CO2 laser.
This just recently started as I have burned things many times without this issue.
I am running the burn at 200mms and 10% power.
Below is an image of what is happening. I have checked all the pullys and belts and everything looks fine.
Pretty sure its a machine issue as I had a VMSTech board in it a couple days ago and had the same issue, so I switched that out for my Cohesion3D board and it does the same thing.
Any help would be greatly appreciated.

If you’re absolutely certain that your mechanics are good then you may be losing steps at the motor. Can you hear a buzzing from the X stepper when this occurs?

Try tuning the acceleration values. Run a series of tests starting from a low baseline. Increase until you’re able to willfully cause skipping. Then back-off a couple of degrees.

I will check the acceleration values, but I have been running these same settings for almost 2 years with out this issue. Could it be the motor going bad? Or m I running it too fast at 200mms?

Possibly. Have you ever run at these values before?

I thought you just recently swapped the boards. Is that not correct? If so, did you go through the process of normalizing all GRBL configuration?

Yes I have run at these speeds before, I did swap the boards and one is GRBL and the other is Smootieware, I had the VMSTech board in first and had power issues and then the shifting issue. I put my C3D board back in and tried the same project and had the same shifting issue, I went back and looked at both burns and while they both had shift issues there were not in the same place during the burn but close.
I just ran a similar project with the same speed and power (not the one I had the shift issue with) on a scrap piece of wood and it came out perfect.
Then I loaded the original project back into LB and ran it on a scrap piece of wood and it also burned without issue.
The issue appears to be intermittent , but this issue has happen all three times I tried to burn the same project on slate coasters.

If you’re having these issues with the same equipment and cut settings then I’d suggest revisiting the mechanics.

Make absolutely certain that all pulleys are properly secured. This may not be entirely obvious. Check belt tension. Look for any mechanical linkage and make sure not only that they’re tight but properly connected.

I’m not familiar with a failure condition of stepper motors where they would gradually lose performance but I suppose it’s possible.

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