Reference on combination in front office product page prestashop 1.7.7.6 not working

Reference on combination in front office product page prestashop 1.7.7.6 not working

Hello Everyone

When I change a combination in front office product page of my prestashop 1.7.7.6, the reference of product not change,
the image of combination change but not a Reference

How can i fix this ?

Thanks in advance