The area of polylines with arcs can be incorrect.
With only line segments it is correct as far as I can check.
See <Poly-line Area.dxf> ; <Poly-arc Area.dxf>

It does not depend on the quadrant their in nor with what point the start point is.
It is related with the oriëntation.
Flipping or mirroring horizontally induce the error.

Modifications like flip, move & copy may induce another error that locks the oriëntation.
It is noticed that the oriëntation property in the editor does not change anymore when reversing.
Although locked the value of the area property switches between good and wrong.

The master poly in question is a part of an arc and a part of an ellipse exploded 1024/full.
These where recombined to one poly with 'Create from selection' and are closed.
Closed as per the last vertex does not point to the start point, logically closed I presume.
The purpose is to sum the error surface for the skewing math.
For now I will use my common sence to distinguish what value is the correct one.
Reversing while found faulty is the solution.

Version: 3.20.1.0 (3.20.1)
Internet: QCAD.org
Build Date: Apr 13 2018
Revision: dd51609
Qt Version: 5.5.1
Architecture: i386
Compiler: MSVC++ 10.0 (2010)
Win7 32bit

Regards