A lot of plastic collects at the bottom of Ultimakers over time. When moving the Ultimaker 3, it's quite easy for this material to get stuck on top of the Z endstop, creating issues with bed levelling. I created this guard / ridge to prevent pieces from sliding there in the future. Created based on manual measurements and the Ultimaker 3 bottom plate 3D model: https://github.com/Ultimaker/Ultimaker3/blob/master/1944/1944-F/