Strange issue with variations

Hello,

I have an issue with my variations. I have set up a variation on my Woocommerce store nad the variation is shown variations page (Products-Variations). However, some latest imported products do not appear to be linked to this variation and therefore are not shown in product filters. They do show the variation when I select the item on the store and clients can order the product (select favourable variation of it and I can see what the client selected).

The products do have different reference under “edit” option:
Screenshot of the product variation not linked to the store variations
Screenshot of the variation linked to the store variations

What might be the issue here? Why some product variations are linked to the store variation I created beforehand and some are not, just a list separated with vertical line?

How could I amend that?