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I'm experiencing a very annoying issue that seems to crop up randomly. I cannot correlate it with anything in particular.

My prints will randomly have pitting evident on the exterior surface (photo attached). I believe this is due to inconsistent extrusion. I've been using both PLA and ABS on this print head and I'm starting to wonder if that's a bad idea. It seems to become a problem more often (not all of the time) when I switch filaments. Has anyone else had any experience with extruder issues when switching between PLA and ABS or other filament combinations?

I'm theorizing that the two plastics (which melt nicely at 20C apart in my experience) are just incompatible enough that they will cause minor buildup that will become an issue intermittently but not a full blockage when switching between them.

Thoughts? Thanks for your time and brain droppings.

I'm currently having the same issue, I only use PLA though so I don't think that the problem.
In my case the extruder seems to intermittently pushing the filament.
Marking the filament with a sharpie then manually extruding 100mm I can see the filament start stop start again and so on, yet to figure the solution though.
I've cleaned the thing and stared at it, so far that's not fixed it.

I am experiencing a similar behavior.
I am looking into some temperature controller issue and/or filament quality.

In the first case, it could be that the power supply is not delivering enough voltage. So as per geneb recommendation, I checked the power wirings between the power supply and Rambo board. I found some under-voltage (around 10V instead of 12V).
Before I am able to fix this I will also double check the temperature probe gain law in the firmware as I did not change it despite the hot end and probes replacement (upgrade to HE280).
The pictures are showing some sort of "intermittent" extrusion. The weird thing is that with the same filament, but different color, I printed smoothly.

Francesco