Error Code=2 "Cannot connect to iTunes Store" {NSLocalizedDescription=Cannot connect to iTunes Store} only in production env for some users only

Question

I have implemented Auto-renewable purchases in the App. But, not all the users are able to complete the purchase. Their money is deducted but the transaction goes in the failed state with the above error, or sometimes it does not even trigger the updatedTransaction method after purchasing state. Also if I ask the users to restore the purchase, they get an alert as "product already purchased". I am very frustrated with this now, as I can't even replicate the issue. It works perfectly on a sandbox, plus I tried the real purchase and it worked there too. What is that I am missing? Please help me.