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?