this only happens in uccnc and only if the program is executes as a whole, on single line or via MDI the movement is fine
I see, but this unfortunately means that something is fully wrong with the step/dir generator, because the G81 is executed from G1 codes and so then if this issue happens then G1 codes should have the same issue.
You previously wrote that you using a different breakout board for the UCCNC and for others, can you try the uccnc with the same breakout board as you using for others for crossing that out as a possible source for the problem.
And meanwhile if you will send me the .pro profile file then I will give it to my collegue to test and measure it.