Hi John.
It looks like your rectangles are over traveling on the x-axis too and it isn’t just the text that is having a problem.
You say that it was working very precisely BEFORE you adjusted the eccentric lower wheel. I had to make a similar adjustment due to a tilt in the laser module. I posted about that in the Creality Falcon forum in the Falcon 2 Laser Head Tilt - #13 by Wet.Coast post. BTW, you might get a better response to your posts on the Falcon if you put them directly in that forum.
The problem looks like an x-axis travel issue and not something that would be related to a dirty lens. I’m guessing that you’ve confirmed that there is no wobble in the laser module at all and that you haven’t over-tightened the eccentric lower wheel nut.
You didn’t say what your settings were when you ran these tests. Have you tried a lower travel speed and power setting? I only have the 22W model and I’m wondering if with the 40W model, the temptation to use a faster travel speed is causing an issue here. Just a thought.
@Zolt, do you have any ideas on what might be going on here?