If you know that a product is contained within your index, but it's not appearing in search results, first check if the product was indexed with an algolia_ignore tag. Removing this tag should mean the item is displayed in the product in searches.
You can also verify:
If the products are part of the Online Store channel?
And that they are 'Published'/'Active' and not marked 'hidden' or 'ignored'?
Also, if they were marked 'Available' using the batch editor tool?