Printer Stops extruding mid Print  

Printer Stops extruding mid Print

Hi, im having troubles lately with my printer and im running out of ideas

Printing with fillamentum PETG at 240/90

Problem:

Printer stops extruding mid print. It seems to happen when the layer print duration decreases rapidly/when the printspeed is reduced to keep the part cool enough.
The extruder gear grinds a gap in the filament while It tries to extrude.
This does not always happen on the exact same layer but its not random (pictures should proove that)

I replaced the following parts:
nozzle, heater cartridge, Heatbreak screw inside E3D Hotend, PTFE Tube and the extruder Gear

I also tried disabling retraction but it didnt do any difference.

One of the pictures belows shows the end of filament after unloading it. It seems that the last part has a slightly larger diameter as it was already heated a bit. This could be the reason as after loading filament again the printer extrudes just fine.

IMPORTANT:

My printer lives in an enclosure and was working fine for several months. The temperature inside the enclosure is around 45°C
The printers behaviour seems to depend on the surrounding temperature: When the enclosure door is opened, most of the prints go well.
I already installed a fan to my enclosure but Id like to find the source of the problem rather than to minimize the number of failed prints.

The resulting failed prints can be seen in the pictures (it happens stls independent)

Thanks for your help