Could you please try going to Wp-Admin -> WPML -> Settings -> Custom Field Translation for a field related to product galleries "_product_image_gallery" and set it to "Copy".
* You may need to click "Show system fields" for the field to show up.
Please check the attached images to see which section I am referring to.
I checked on WPML -> Support and noticed that the WP Memory limit is 40MB, could you please increase it to at least 128MB as WordPress uses 40Mb as default and the minimum requirements for WPML are 128 MB?
* Note: Please make sure you have a full backup of your website before making any updates/changes to your website.
After, please try clearing the website's cache (server-side included), and try making a small change (ex: add a "+" sign to the title and remove it again after you have updated the product) to a product you already translated and has the gallery images.
Can you check if the translations update without adding the "+" sign, just by clicking "Update" when you edit one product? Try with a product that is already translated and not with one whose translation needs updating.
* I noticed from WCML that some product translations need updating.