Updated to the current Luban and OS for the A350 and came across an issue when selecting build plate adhesion and support.
Support, the ‘skirt’ was fine, not selecting support and the skirt was way too small.
I ran the same file through Cura and the skirt was okay both ways.
Any thoughts?
Stop looking up Luban’s skirt. 
Anyway, without having access to the actual model, what usually causes that is the base isn’t actually flat. Only the one corner is touching so it’s drawing the skirt around what it thinks is the entire first layer. When you enable supports, it makes a much larger first layer (the supports first layer) so it runs the skirt around that. Looking at the first image, with supports, it looks like the bottom is angled up. You need to rotate it so that face lays flat on the bed, I’m not sure if Luban actually has a lay flat tool built in.
I auto rotated as well as manually, same outcome, took a look at the file in Fusion all parameters line up.
Opened and sliced in Cura without issue.
Like you I’m thinking it wasn’t seated flat, but strange.
