I would say less then 3% of all the offers done on QR are placed on hold. It also depends on the offer. Sometimes it could be 100% of the signups for a certain offer are placed on hold. Some offers take a few days to report so we have them pending until they report. Sometimes an offer does not report because cookies were not cleared or something didn't track and would require manual credit. We pend them until the credit comes in. There is no exact answer to your question because it depends on many variables. All I know is that if an offer is on hold that does not mean it necessarily didn't credit correctly or it does not mean that you not getting paid for it. As soon as the credits come in (some take a day and some a few weeks) you will get credited.
If your transaction is on hold because it is missing we do our best to get the manual credit asap, but sometimes it is way out of our hands. What I think makes QR different then most other sites is that we actually follow up on missing transactions (most other sites have a policy if we dont get credited, you dont get credited period) and a lot of times if we cant get the issue resolved or if we think it is impossible to resolve it we will just issue you the credit without getting paid from the advertiser.