Hi! First of all, excuse me by my bad english.
I'm a Cura user since 2018, and for about 6-8 months I saw this kind of bug in Cura.
The STL is fine, it doesn't have errors, but sometimes a layer is missing and it appears on the floor. If you move the model a little it fixes.
The same happens with the supports. It's like there is an imaginary grid on the floor so you have to move the model to fit in the grid.
It doesn't bother so much because I always watch the Layer view, but sometimes I'm in a rush and find the Printer doing supports mid air and it's a problem.
Thank you ve