The review system only submits results to the server one item at a time when you’ve answered both reading and meaning correctly for that item. Everything partially done (i.e. still awaiting a correct reading or meaning) is stored in browser cache. But the cache is only good for 1 hour (I think), so as long as you retry your reviews within an hour, it will remember your partially-done items. If it’s longer than 1hr, you would normally have to redo some reviews.
It shouldn’t ever mark a result (either correct or incorrect) if you didn’t actually complete the review, regardless of signal loss issues.
If your queue says you have zero, and you think you should have some, I’d recommend clearing your cache to see if that has any effect. The API could also show you what reviews it has on record, but you’d have to know how to extract the info.