Ravi1

Can someone advise what could be the cause of my rear toe alignment not adjusting. Could it be a bad knuckle rubber/bushing? (not sure if that applies to the knuckle). The mechanic is stating that when turning the bolt he can see the alignment going where it needs to be but then suddenly just pops back to where it was at the beginning. Currently been through 2 pairs of tires for the rear (on my third pair) and I want to fix this before buying another set. Any help would be appreciated. Picture of the part is attached. the toe bolt goes through one of those ends at the double rubber and the upper control arm connects to the end with the single rubber.