I get that the issue isn’t actually caused by Monzo, but the the negative result of the issue is experienced in the Monzo app.
I think that if Monzo are unable to get WorldPay to fix the issue with Tesco transactions, then there must be a way that Monzo can mitigate the issues by improving the UX here somehow.
If Monzo receive an authorisation code from Tesco to settle a transaction which doesn’t match a pending transaction authorisation code, then surely they would know there is a mismatch?
I wouldn’t have thought there would ever be a legitimate circumstance where you’d buy something in Tesco and the transaction would be put through for an immediate completion without a pre-authorisation?
I have zero knowledge of these things clearly but I would have thought there would be some way for Monzo to intelligently match up these mismatches instead of displaying a duplicate transaction? Maybe that isn’t possible 🤷
Because I’ve had so many duplicates in the past few weeks, it’s become very difficult keep a track of the duplicates/refunds. Part of this is that the refund transaction doesn’t tell you which transaction is refunded, and the original transaction just shows as pending forever instead of updating as refunded. I have had to use tags to keep a track of things but even that hasn’t been perfect.
As I mentioned before, I had to raise a dispute a few days ago because instead of refunding after 8 days, one of them completed. Within 24 hours of raising a dispute, a refund came through, so I thought it was as a result of me raising the dispute. However, yesterday I got a notification saying my dispute is now in progress, and at the same time another refund of the same value hit my account, so I think I’ve been refunded twice for the same transaction now. 
This is what I mean that it’s becoming difficult to keep track of, as I cannot determine myself exactly which transaction a refund is for, other than it matches the value. When you click on an open dispute, it doesn’t even link back the transaction in question, so if you happened to have more than one of the same value, it could be very confusing.
I contacted support in the app on Monday, and was told someone would get back to me within 8 hours by a front line cop, but it’s Wednesday now and I’m still waiting.
I know Starling have a lot less customers than Monzo, but Starling also do instant notifications I believe? And doing a quick Twitter search I am not noticing any Starling customers raising this, but numerous Monzo customers over the past few days.
Sorry that’s so long winded, but I just have to believe that there’s a way Monzo could make the UX of these data errors caused by WorldPay/Tesco better.