Product listing + Module

Hello,

I have the following problem.
After all the products listing I have a module which displays random products from the same brand.
Let's say that I have a paint marker with a product code exp1.
I have created that marker long ago and now I want to display the colours as variants, with different product code in each variant.
After I modify the old product, the module in front-end displays random products from all the categories, not from the same brand, when before worked properly.
I have set the right brand to my new product, with the variants.
Why is this happening?

Thank you in advance.

Hello,

Here is the link with the problem.
The second module under the product listing displays wrong products.

1,2 photos are the module and 3,4 the product.

Thank you in advance.