Donner not cutting through

I was there yesterday afternoon and tried a project I’ve done several times in the past with 1/4 ply and the laser wouldn’t cut through the ply. Checked the power/speed/height…all seemed fine and exactly what I’ve used in the past with no problems. Thoughts/ideas?

Lenses/mirrors probably need to be cleaned. Also depends on material moisture (when relevant), and also depending on how long ago you ran it, tubes slowly lose power over time.

Are the lenses/mirrors something I can learn how to do? If so, how and where? Yeah, I try to avoid long projects at once because of the power loss. I break up my projects so the laser isn’t running for more than a minute (at most) at a time, then do the next project, etc…