ceoloide

Hello All, Sorry to resuscitate this post. I am having the exact same issue with a brand new Ultimaker 2. I consistently have something like a missing layer between 10 and 20mm. This happens reliably, even when using different 3D models, speeds and using two different PLA filaments (printing at 210 degrees). What is the suggested solution to the problem? How to ensure that this is indeed a mechanical problem? Thanks everyone for your help! Marco