Issue with display off variable products created programattically

I’ll try keep as brief as I can – developing my own plugin which creates variable products on the fly.

When created and then viewed on frontend I get the “This product is currently out of stock and unavailable.” message. Everything else is all good and product appears fine in admin etc, I’m running
WC_Product_Variable::sync( $new_parent_product_id );
and it’s doing all that I’d expect. If I update the product in admin without altering anything then it displays fine on the frontend.

Working back through the product templates to variable.php I see that $available_variations in there is empty. Digging into class-wc-product-variable.php noticed when I log $this->children in there the get_children function a product that’s not displaying returns:

$this->children in get_children : Array
(
    [all] => Array
        (
        )

    [visible] => Array
        (
            [0] => 550
            [1] => 551
        )

) 

Once I save/update in the admin and it displays right I get:

$this->children in get_children : Array
(
    [visible] => Array
        (
            [0] => 550
            [1] => 551
        )

    [all] => Array
        (
            [0] => 550
            [1] => 551
        )

)

At this point I’m stumped and get a bit lost in the code! I just can’t see what’s causing the [all] array to be empty (or why array keys are reversed)??

Massively appreciate any further pointers, have been stumped for hours & hours on this!

Cheers,

Steve