Waviness, as I see it, is like moire in the screen printing we did.
It’s an interference pattern the result of two different frequencies occasionally hitting the same values, and then slowly moving away, then merging again etc.
You can hear it in guitar tuning when two strings are not quite in tune, but are plucked together, there is a waaw interference pattern sound.
If you have an original file at 300 ppi, and you laser it at 600, or at 150 ppi - direct multiples of the original, you’ll seldom get those issues.
If you chose to laser it at 254 ppi, which is 10 dots per millimetre, you’re going to get an interference pattern because 254/300 is not a neat integer (whole number).
However, that won’t be why the bottom of your file is shifting out of kilter.