I had a transaction from Guardian missing before. I tallied the cashback and realised that it's lower than what I expected, called in to UOB to ask. They mentioned that it would take 3 days to retrieve the statements for the 3 months, and would double check and call back after that. During the callback, the CSO went through each transaction that qualified for the extra 5% cashback, and I realised there was 1 Guardian transaction missing (about $3 of cashback). It was weird because other Guardian transactions were included in the extra cashback computed. The CSO said they would adjust and credit the extra cashback to me (the call was on 22 Nov) but until now it still has not shown up on my iBanking, so I'm still waiting.