Hook Spring
WARNING: This page is about a different car, the 2021 Subaru Ascent. However, it is still accessible from the selected car via links, so may be relevant.
Check the flat mat hook spring by applying weight to the backrest assembly.
NOTE:
If the appropriate stiffness is not obtained by applying weight to the backrest assembly, the hook spring may be disengaged.
If it is due to the deformation of the hook spring, replace the flat mat & hook spring assembly with a new part.