I tried cutting paper but some lines were randomly not cut. I formed the theory that the reason could be, that the cutting starts too late in some cases, when the movement speed is high (I did the cutting with 650mm/s when noticing this - at 700mm/s it gets worse).
So I created a test svg in Inkscape and in deed, it turns out that in some cases, the laser is firing up late, causing cuts to be incomplete, see this photograph of my test here:
As said, settings were 650mm/s, no repetition of the cuts. Since the delays show up at random, repetition makes the problem go away, which is however not how I would like to see this solved.
I’m pretty sure that this is a bug.