[UM2 stops printing outer shell]

Hello everybody,

After printing several batch prints, my UM2 printer starts to print weird.

I'm trying to print 4 small hooks so you can hang frames to a wall.

The first one is printed normally, but the second one misses the outer shell.

The third and fourth one are completely messed up.

How can this happen?

My Cura settings:

Layer height: 0.1 mm

Shell thickness: 0.8 mm

Bottom / Top thickness: 0.6 mm

Fill Density: 80%

Print speed: 30 mm/s

Initial layer thickness: 0.3 mm

Initial layer line width: 100%

Travel speed: 150 mm/s

Bottom layer speed: 20 mm/s

All the other speeds: 0 mm/s

Thank you for your help