I definitely get that you are annoyed that you have to go through the process of offer validation together with the offer provider but as I explained - this is necessary.
Now in regards to the frequency of the issues - I have enough data from the support team to know that issues with offers are not wide spread. In fact we get few reports of such cases on a monthly basis. Also we consolidate the data with the offer providers in order to establish what is the frequency of offer issues across the board.
With that said, do know that due to our communication with the providers, they constantly upgrade their systems which seems to be giving positive results. There less and less cases with missing rewards than there have been in the past.
But to reiterate. If an issue arises, make sure to tell the providers. They'll provide assistance and register the case which will be helpful in the long run.