Today an ATM withdrawal transaction was reversed, adding £40 back into my account two days after the withdrawal. I wish this was a feature and not a bug.
This is the third time an unexpected refund has happened, first time the merchant never reclaimed the money, second time they did… here’s hoping that the cash point will not re-charge my card!
So Monzo is mistakenly reversing your withdrawals, it’s not the merchant refunding you by mistake? Have you checked this with the support team? This has never happened to me but I wish it had! 
The first time Monzo support said that if a merchant takes a contactless payment and doesn’t do an additional confirmation within 7 days, the transaction is automatically reversed. However the ATM is something else, maybe I should delete this post.
I’ve had this too when a Tesco ATM took ages to finalise the transaction. It was refunded automatically, and then later completed as a separate item in my feed.
I had the same issue and the money was extremely important and even though the owner of the cash machine said the money wasn’t debited it was taken from my account and now it is going to take up to 7 days to return the money so I have been left in a very difficult situation
How long did it take to get your money back from this issue
This doesn’t sound like the same issue at all. The OP has been refunded even though they where able to take the cash. You should consider starting a new thread specifc to your issue Instead of resurrecting a thread that is four years old
OK I’ll make another post