I am currently finishing my PhD in rancidity, so ... let's say I know quite a bit about it. The picture is not a fair representation of what happens, since free fatty acids should be present, though you just show the triacylglicerols. Which rancidity happens first will depend on the matrix and on the storage condition of the oil. Usually, but not always, oxidative rancidity happens first.

Regards,

Lourdes