I am creating a dynamic block of a conveyor belt

There are a number of parameters I am including, firstly a set of 14
different standard widths, and also the length needs to be able to be
stretched to any dimension, whilst keeping certain elements (motor, legs
etc) centralised

I have drawn all the different standard widths and then created a block
from that, I then went in block editor and laid each different width of
conveyor directly on top of each other so that they all insert about the
mid point of the width

I created visibility states so that each width of conveyor is able to be picked from a drop down list

The problem I am having is with the stretch command

I went back in to block editor and applied a length parameter and did
the stretch command as normal. I then saved the block definition and
closed block editor, but when I come out the stretch command had not
worked, no grips or anything, like I haven't even applied it

When I go back into block editor the grips for the stretch are there

Any ideas?