product.collections stopped listing all collections

We're using this property
https://help.shopify.com/themes/liquid/objects/product#product-collections

which used to work fine until a week ago. It doesn't work anymore properly on 2 stores, but works on others.

store1:

This product is part of more than 10 collections, set at visibile in store.
https://diamond-pride.myshopify.com/admin/products/12141012228

Please preview the Blank theme, it has ONLY this code, to avoid any doubt:
https://diamond-pride.myshopify.com/admin/themes/205389828?key=templates/product.liquid

product.title {{product.title}}
<br><br>
  
{% for collection in product.collections %}

collection {{ collection.title }} 
<br>

{% endfor %}

It shows only 2 collections, instead of 10+:
https://www.diamond-pride.com/products/russell-premium-ladies-t-shirt-stuttgart-reds-softball-heather-grey

store 2:
https://lakukan.myshopify.com/admin/products/11896568725
is part of multiple collections, all visible in the online store.

https://www.artsalwa.com/products/dua-when-leaving-washroom-polkadots

Please preview the Blank theme:
https://lakukan.myshopify.com/admin/themes/189759509?key=templates/product.liquid

View that product in store:
https://www.artsalwa.com/products/dua-when-leaving-washroom-polkadots

it shows NO collections

Expected:
list of all collections the product is part of, attached

Shopify support and themes@shopify don't want to look at this report, directed to forums instead.

Use the product.liquid snippets and linked storefront examples as the reproduction entry point; compare product.collections output with the reported collection membership. Check whether the expected result—listing all visible collections—is reproducible, then identify the relevant Liquid implementation and add coverage for the reported behavior.