This is because you closed the account before the money was actually even transferred so it canceled & reversed the payment as it gets classed as declined but since you don’t have your account it can’t be returned to you.
You’ve temporarily lost the funds and it’ll need investigation which can take a week or so in my experience
Usually when a payment has cleared it’ll actually be in the account rather than showing as incoming, when a payment shows as incoming it just means a payment has been arranged but not processed by either end.
It needs a deep investigation and the 8 hour will just be for a response which could ask for evidence that you haven’t received the funds or even the reason you closed the account instead of switching.
As stated above it looks fishy. You could be laundering for all they know.
Remember we’re all just guessing here so what will happen will happen. I don’t recall seeing this scenario come up here before so unless someone’s experienced it for themselves we have very little data to work with regarding what to expect.
I had read a number of posts that advising Monzo if making a transfer that isn’t just a couple of hundred £ to avoid chance of an account being frozen. If that’s poor advice, that’s fine, doesn’t do any harm anyway.
I advised Monzo about the transfer and closing the account, yes.