I was got this issue (Purchase Requisition did not collected on ASCP Oracle) even when i doing standard collection complete refresh.
after struggling for more than five hours i finally found out in the one of the log files, and some select whether the PR is really exist or any wrong setup either on ERP or ASCP Setup
found out that the setup or profile MRP:Consume MPS Should be set ‘No’ instead of Yes
you can change this setting on Responsibility ‘system administrator>> Profile >> search for %MRP%MPS% then change the Profile Option MRP:Consume MPS from yes to NO
after that you should try to submit collection and make sure the purchase requisition already collected