I installed a fresh Magento CE 2.1.6, I can import about 2.500 products using the import function as usual.
My only problem: When importing images, the categories do not show pictures, only broken image links. In product view, images work fine.
When checking the category view, I find that the images linked which are supposed to be in a cache folder are not present.
As soon as I manually attach the tag "small" in the product management to a single products, it works fine.
I did cache cleaning etc. I also imported just a few article images to exclude memory or time limit problems. Running a large custom server without load issues.
Any ideas? I would also be glad to set the "small" tag in the database, however even after browsing for a while I don't see where this tag is processed in the database.
Best is to add small image in the csv import file. It'd save your time and apply the right images to your products.
I recently managed to import more than 10K products and it all went fine.
I hope this answers your question.