Random letter-spacing

Hi

When printing labels using a Zdesigner gk40d we get some random letter spacing.

It seem to be certain combination as an example if "k" come after an "a" theres a space". But if "k" come after lets say "r" there is no space.

And as stated if a came BEFORE k theeres a space but if a comes before r there is not.

I have attached example.

Any suggestions on what could be the issue?

Thanks!