Diagnosing an issue with 2 month old P1s

Bambu Lab P1 Series Troubleshooting
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UPDATE - always check another spool of filament… despite me probably having used 50+ spools of elegoo pla+. This particular spool for whatever reason doesn’t seem to be able to print at regular generic PLA speed. I was so set in the assumption that it couldn’t be the spool that it must have been the printer. So after re-tensioning and replacing the hot end, I think it’s just one duff spool of PLA…

ORIGINAL PROBLEM:

All of a sudden my prints show issues on prolonged extrusion sections, such as bottom and top layers of relatively large surface areas.

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I’ve added an image of the problem.
One print of this object was fine, the next suddenly became like this.

I have cleaned the carbon rods, and I have re-tensioned the belts 3 times, and ran recalibration after each. In fact the two examples in the image are before and after the re-tensioning with almost identical results using two different textured bed sheets,to rule those out.

The corners where the movement is quick before it reverses doesn’t seem to have the problem, only in the middle.

The exact same gcode ran on my other (14 month old) P1s works perfectly, with exactly the same Elegoo PLA on generic PLA settings.

If left to run the print ends up like this on the top and right edges, but perfect on all other edges.

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What I am about to try is replacing the print head in case there is a strange clog of some kind.

Are there any other suggestions you might have? The top right edge is where the walls start and end…so could it be the extruder gear is knackered on a 2 month old machine?

Many thanks for suggestions!

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Usually those ripples on the first layer occur when the nozzle is too close to the print bed. Solutions you can test: increase the z-off set in the start g-code in the printer settings. Check in the slicer if you have set the correct print bed which is installed on your print bed. Try printing with a different filament and see if the same problem occurs again. Check if the nozzle assembly is securely fixed in the hotend… I don’t think it’s a problem with the guides or belts. Let me know if you solved the problem by lifting the z-off set and after checking the rest of the probable solutions above.

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Thanks for the reply - I added an update to the top of my original post after I changed the nozzle.

It turned out to be a strange roll of filament. Elegoo PLA+ always worked fine for me on the generic PLA profile, but this particular role exhibited these specific symptoms, never had it before and I use these rolls a lot, so it didn’t even occur to me that it could be the specific spool.

Hopefully those that may end up here from googling will be helped in diagnosing future problems…as it really does present as a problem that isn’t typically consistent with a filament issue.

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I came across something similar doing a larger print with Elegoo Rapid PLA+
I had a feeling it was the roll since other stuff has come out without issue before and even after. I guess another point for Elegoo having some inconsistencies.