1 in 100 purchases don't activate my in-app content ?

Hi, this is difficult to reproduce, because it happens so rarely, but customers get really upset about it when it happens, so would be good to fix.

Are there any common reasons why this might happen ?

What happens is that about 1 in every 100 users experience that in the shop, the IAP's get ticket off as purchased, but the actual content (when in the main interactive scene), isn't unlocked. It works fine for the other 99 users. Those experiencing the issue, need to completely close the app (double tap home, swipe the app up), and start it again, or just reboot their phone, and then most times it is fixed.

I'm using the SimpleIAP (iOS) implementation from Rebound Games, and contacted them first, but am being told that "Overall, things like that (pending transactions) happen and there is not much to do about it, since its pretty much out of your control."

So is this to be expected or what ?
Is there something I could do in app ?

Unity version 5.5.1f1
Unity IAP ## [1.9.2] - 2016-11-29
iOS

Many thanks in advance!

 

Hello? Could some kind soul please let me know if this behaviour is to be expected or not ? Thanks!