Sorry, hadn’t scrolled up before responding on that last one. Did you also check the mirror?
How is the new post cleaning one turning out?
Almost same as pre-cleaning. 
Looking closely I think it is slightly better, but looks nothing like how it has looked for the last couple of months. It appears to cut deeper and perhaps wider. Is it possible that focus has always been off, and I just happened to now randomly fix it, so it doesn’t match what I’ve printed before? 
Manual focus on the left, auto-focus on the right (I’m ignoring that one for now - as I need it to match what I have printed earlier).
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I did check the mirror after cleaning all the lenses, and it looked spotless so I didn’t do anything to it.
I think it’s time to switch to proofgrade (it has a finer surface) and make various thin lines to better evaluate the focus… Will try scoring instead of engraving since it’s 1000x faster.
Good idea. At this point I don’t know of anything besides variation of some kind in the wood or wood glue in the plywood that could cause the differences. But if they are on the same sheet, it would be pretty unusual.
Thank you for all the input so far. At least I’m probably not going crazy (yet).
Will post once I have tested some scoring. But I live in an apartment and its’ 10 pm, so even with the compact filter I don’t dare to print too late… 
I have seen the Laser mess up on less. Make sure that it is not just stuck and you may need another lens.
Just to clarify… if setting the material thickness (for non-Proofgrade), if you set the focal height to the same value, it will use auto-focus, or, at least that’s always the way that it has worked before. To override the autofocus, the focal height needs to be different than the material height. For example, 3.6mm material height and 3.5mm focal height - where the 3.5 will be respected.
Hmm, that’s interesting. It might have changed then considering it looked even darker when I used auto-focus (material and manual focus were both 3.6 mm). Will have to test that separately tomorrow.
What can cause a blemish like that? Nothing has touched the lens, and it (the quality drop) somehow happened between two prints.
Edit: I got it off.
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One more variable to consider is whether or not your material is completely flat to the bed. Here’s a good post on the subject…
Manual focus will exacerbate focus issues anywhere the material is even slightly warped.
One more variable to consider is whether or not your material is completely flat to the bed. Here’s a good post on the subject…
Already considered. There is some warping of these poplar pieces that I am fully aware of. It’s within a certain range at least, and I have tried to use the flattest pieces and position them as best I can. But the surface height variation has not caused any variation nearly this large. I have printed a whole stack of these pieces cut from various parts of the board over a long period, so I know.
Here are some of them, and the bottom right is how it printed today:
(same piece of wood, same settings - the grain direction and light made it look a bit brighter)
It seriously looks like the difference between material you’ve cleaned the soot off after engraving vs straight out of the machine - there definitely shouldn’t be so great of a difference with the same settings :-/
I’m hoping if none of the things suggested above help that Staff can look at your logs to see what’s up in the background!
Yeah, and if you look closer at the bad piece, the “planet surface” should all be the same medium/light color (it’s all a single shade in the file), as you can see if comparing it to the light shade on the other pieces. Yet on the bad piece it varies between very burned and full of white specs…
Good news though. With some gentle convincing I was finally able to get that last speck off the lens. It’s late now, so I will not run new tests until tomorrow.
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Really appreciate all the work documenting this puzzling situation. I hope it all works out. It is weird when something different happens from what is expected and customary. So many possibilities. A good trouble shooting example here.
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I wipe the 5 mirrors/windows every morning that I cut. Takes less than 2 minutes, and then I’m absolutely sure they are clean.
It is printing correctly again today. So might have been that tiny speck on the lens that was responsible! 
Thanks for all the help.
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Thanks for the help everyone!
@jonas1 I’m glad everything worked out! I’m going to close this thread. If you run into any other problems please either open a new thread or email us at support@glowforge.com and we’ll be happy to help!