Algolia for Magento 1: Some product thumbnails aren't being created in the dropdown results

In our Magento 1 integration, some product thumbnails aren’t being created. I have tried to clear product image cache and regenerate the thumbnails but to no avail.

Has anybody come across a similar problem?

Hello Ivan,

did you try to reindex those products without thumbnails? Did it help?
If not, could you go through your Magento log files and check if there is any image generation related error?