I chatted with their UOB digital assistant. The CSO said they are in the midst of investigating the issue and will credit back the shopee rebate. We should receive an SMS when they do so.
So, this is already a known issue on their end it seems. Just need to wait for them to rectify the issue.
this reminds me of a similar perpetual mistake made by standard chartered on the use of the ez auto-reload for their credit card. in their tnc, it was printed clearly that auto-reload using cc is eligible for their 1.5% rebate. but every month the statement will exclude those transactions and end up every month i had to write in/call to their CSO to have it manually credited back. i think i did that for like 4, 5 months in a row until the bank decided to terminate ez re-load feature in the card since Jan this year. (and i stop using the card since)
tl;dr when it comes to rectifying mistakes in the system it is quite appalling how primitive and manual they are. won't be surprised they will also be doing manual crediting for those who bother to 'complain'... they must think that most customers don't bother to check!
worse is when their CSO is also half-baked in their knowledge and understanding of the products and try to give lame excuses or wrong facts to try to cover up the mistakes (like what zenical mentioned, accusing customers of using shopeepay when it is not).