.... Your FACTORY-FILE please!
Sorry, wich one ? the print profile is the default one for geetech A20m
Extrusion multiplier 0.9 (default is 1.0)
Layer height 0.3
Outline speed 50%
Retractation 6mm at 30mm/s
NB: stairs disapear totally in vase mode.
Also stairs height seems to be 4 layers height and retractation occur on each border every 4 layers ( according to simplify3d preview ), so maybe related to retraction or over extrusion as you mentionned, dont know I already lowered extrusion to 0.9...