What might cause these effects?

Calibrate your extruder as mentioned by @rick (Thanks Rick :smiley: )

Here’s the tutorial on how to do it (I did it with Octoprint, but it can be done with other slicers :slight_smile:
https://mattshub.com/2017/04/19/extruder-calibration/

And here is the original post by Rick :slight_smile:

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