Hello,
A few things to double-check on your side:
1. In the Google Products plugin settings, confirm that "Include variants" is set to Yes. Without it, variants are not exported at all and Google Merchant would flag the main product listing as missing a variant breakdown, which can look like "missing photo on variants".
2. On the main product, the pictures need to be uploaded as Images, not as downloadable files. The feed generator only pulls entries where the file type is "product".
3. Use the "Download now" button in the plugin configuration to export a fresh XML feed, then open it and look at one of the variant <item> blocks. Is the <g:image_link> tag present, absent, or present but pointing to a URL that returns a 404?
If the tag is absent on your side, please share the exact parent product configuration (number of images, where they are attached) and we can dig further. If the tag is present but points to a broken URL, the issue is likely on the thumbnail/URL side rather than variant inheritance.