Some designs just will not recover -
there is plenty of fact to back this up
In models - conventional tractor types - typically they are sport/trainers with limited surface throws and aft CG setups.
Visulise what is happening - and where the center of rotation is located.
In most cases there is no air movement aligned with
"flying" attitudes.
My little flat fuselage & flat wing foamies are the easiest types to recover as they have mucho drag and very little weight.
The opposite setups are the worst -
very little side area and/or balanced side area front to rear on the fuselage - does nothing to make the thing want to go back to being an arrow---
you can actually make em climb in a flat spin.