Vcore 3.1 Rear Z arm slides down under weight of bed

Just upgraded from 3.0 to 3.1 on the Z axis, with wobbleX.

As per the title the rear z arm slides down by like 15 cm.
I am unable to home properly unless I manually twist the z hold in place and then home. Then the motors get energized and I'm good.

3.0 Z design had a ANTI-BACKLASH NUT BLOCK, that you could tension to stop this from happening.
3.1 doesn't seem to have any such consideration.

Curious many others wouldn't have the same problem, yet I don't see any posts.
Am I missing something, or some part? Much appreciated