Problems with extruder
Recently I noticed that my prints have portions of layers, or sometimes even the whole layer missing. In addition to looking ugly, it is also a very serious mechanical weakness. This was the extent of the problem until the extruder stopped working entirely in the middle of a print, with almost no filament coming out at all. I attempted multiple cold pulls, which seemed to clear out some debris, but filament still will only come out in normal rates when I manually pushed the filament through with considerable force. The Bondtech gear from the outside is unable to move normally.
Bondtech gear replacement
I've had issues with the teeth wearing out on the bond tech gear. When this happens the gear is unable to push the filament through the extruder. This is especially a problem with abrasive filaments such as carbon fiber.
I assume you have the pressure on the bond tech gear set properly. I suggest checking your bondtech gear to ensure it has enough tooth to move the filament.
I was able to find a hardened steel bond tech gear and they seem to hold up better.
RE: Extrusion
Definitely an extrusion / extruder issue. Check your gears and make sure they line up.
Do this by looking in the door as you load a filament and compare the gear placement on the door and behind the filament.
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Chuck H
3D Printer Review Blog