Etsy accepts a maximum of 10 pictures and a thumbnail. Etsy also does not currently support pictures per variants.
Therefore when you use Nembol to share your Shopify listings on Etsy, what Nembol does is:
Imports your Shopify listings with all their main pictures but with NO variant pictures
Pushes your listings on Etsy, but abiding to Etsy rules and hence removing your extra pictures
This may result in an Etsy listing with fewer pictures.
You can check what Nembol imported by duplicating your product in Nembol to look into it. This action has no impact on your published listings, nor on your source channel (Shopify in this example). We will soon release a product preview to make this simpler.