Use the .align-content-*-stretch classes to stretch single rows of flex items on different screens.
.align-content-stretch:
.align-content-stretch
.align-content-sm-stretch:
.align-content-sm-stretch
.align-content-md-stretch:
.align-content-md-stretch
.align-content-lg-stretch:
.align-content-lg-stretch
.align-content-xl-stretch:
.align-content-xl-stretch