The increase in the resistivity with decreasing temperature followed by a drop by more than one order of magnitude is observed on the metallic side near the zero-magnetic-field metal-insulator transition in a strongly interacting two-dimensional electron system in ultra-clean SiGe/Si/SiGe quantum wells. We find that the temperature Formula: see text, at which the resistivity exhibits a maximum, is close to the renormalized Fermi temperature. However, rather than increasing along with the Fermi temperature, the value Formula: see text decreases appreciably for spinless electrons in spin-polarizing (parallel) magnetic fields. The observed behaviour of Formula: see text cannot be described by existing theories. The results indicate the spin-related origin of the effect.