I'm using Magento 2.3.1. We have 3 store views for multi language. One store view (German language) doesn't display category thumbnails correctly. The other do not have any problems. We tried reindexing, rebuild static content, clear cache. On the product pages the images are OK, the problem is only on the category pages. Any ideas?
I was facing the same issue and I found what is happening at least in my case. I noticed that for products with the issue, the image don't has roles applied.
Just apply roles:
Of course It is a manual task, but I thing a script could be created to update the database (insert values into catalog_product_entity_varchar)