Operating system: window 10 home
Graphics card: Intel(R) HD Graphics Family
Short description of error
1.) The difference boolean will not work properly if the object cutter's normals are outside
2.) If the object cutter's normal is flipped into the inside direction the difference will work.
3.) The user has to flip the applied boolean target's normals into the outside direction because the resulting cut was also flipped because of the object that has been applied.
Exact steps for others to reproduce the error
Based on the default startup or an attached .blend file (as simple as possible).
I forgot to save the blend file. After I retest the boolean difference, the bug didn't show up anymore.
I don't know if that was because of the mesh's size because I already applied the scale.