Hi people,
First thing first, english is not my mother tongue, so redacted this post with the help of "le chat"from mistral, please endulge any inconstancies in the text 
I have been experiencing inconsistent extrusion issues for the past few days: some prints turn out fine, a few are perfect, and others are completely failed.
The underextrusion problem happens on any layer (not only the first/last), sometimes on a small part of a layer, half of it… it seems totaly random.
Since the results did not follow any clear pattern, I conducted 7 test prints under the following conditions:
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Print settings: 0,20mm Standard BBL X1C, print by object with this project : https://makerworld.com/en/models/1465285
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Build plate: changed print positions on Textured PEI Plate (as shown below) Plate has been cleaned with dish soap and perfectly dried before the test.
- Material: Swapped spools in the AMS (Bambu Lab PLA Basic Violet (10700) and PLA Basic Grey (10103)). The filament has been dried before use and the AMS is bellow 22% RH at worst.
I Rated the result from 1 to 5 (1 = perfect, 5 = completely failed, see attached photos),
1 - normal print
3 - a few holes
5 - totaly wrecked
I compiled the results in a picture :
The issue appears to be completely random, with no correlation to the changes made.
Has anyone already encountered this problem ?
Additionally, I encountered a couple time in the last few days an error “The hotend cooling fan speed is abnormal,” (error HMS-0300-0300-0001-0001) which I temporarily resolved by unplugging and reconnecting the fan connector on the PCB. Could that be related ?
NB : the printer is 3 months old, around 400 hours of printing job, everything is stock on it.