printing dotted line

[heizer]

the picture shows the beginning print of an 80mm dia object with PLA. The skirt prints perfect but as soon as the actual print starts the first layer is dotted.
The nozzle actually goes in small steps with retractions in between. I printed the same object days ago and it came out perfect. Immediately after the print with the dotted line I printed a different part with no problems.
Is it possible that the STL file is corrupt all of a sudden? I am using Cura 4.3.