Arrow buttons inverts function in resolutions < 1200px

[guiperalta]

It works perfectly on screens bigger than 1200px, when smaller than 1200px the left arrow takes to next picture (isntead of previous) and right arrow takes to previous picture (instead of next). Tried to find a workaround but couldn´t fix it.

Example can be seen on this link: https://oitentacalcados.com.br/loja/fila-retro-sp-2-0