I had similar problems these past few days. Found 5 blocks in the past 36 hours again, but only got rewarded ~100GRC.
I still don't know how this Wallet hour work. If I am not lucky and no other blocks are found during the same wallet hour in the past 36 hrs, will I eventually get the payment of 100~ GRC for each block found (My BOINC utilization is 90% all the time)?