There are possible many reasons why this could happen, however one step that you can take is to check if the objectID passed is indeed the actual objectID from the variant ID and not the product ID.
In the Shopify's Products schema, the objectID attribute is the variantID which is a unique identifier used by Algolia.
objectID, // Variant id (unique identifier also used by Algolia)
In some cases (especially if you have customisation on the code) where you may have incorrectly passed the objectID as the productID from Shopify.
id, // Product id
Depending on your implementation and relevant use of event methods, both of the clickedObjectIDsAfterSearch and convertedObjectIDsAfterSearch methods for example takes the value of the objectID. These methods are used in our click and conversion events feature within our Shopify extension.
The key takeaway in this situation is to ensure the correct type of ID is used.