I am having issues with a clients site. I am having issues with the menu bar not showing but also the product reverting back to the default size when adding to cart. We are using debut theme and this is an example of a product:
I just looked at the product link you provided. The default size was W22, and I changed it to W44. As you can see in the screenshot below, it stayed the same on the cart drawer. I can also confirm that the size remained W44 on both the cart and checkout pages.
Also, the main menu is visible on my end. Were you referring to the header navigation?