I'm using Magento 2.1.0 with a bought with a template (SM Sawyer) on Ubuntu 16.04.1 Our products are being inserted/controlled by an external registersystem.
After this external source adds products, their thumbnails get created correctly in /pub/media/catalog/product/... At some point after they update certain products, these thumbnails get mixed up in the cache: Once you click on the product you get shown the correct full image, but when shown in lists you will see another product (probably the old cached thumbnail). Once I delete the folder in which this cached images exists, it will start creating the correct thumbnails again.
I ensured the file permissions are on 777 in the media folder.
Does anyone have a clue?