Good eyes!
these gefreiters have perhaps previously set their slings at a good length for bracing while shooting, and are moving up to the firing line at a range? Looping the tab end like that makes a good quick release adjustment, buckle pre set, no fiddling around.
In pic 1 &3, right hand man, the sling buckle is positioned 6”-8” below the lower band, can’t tell about the others.
The men don’t look very young, uniforms are plain, heer tabs, one stripe, no ribbons. Supply or communication troops?