What I believe is that all companies that you purchase with, clear the payment slower than others. This can be due to long processes or slow connection of the card machines.
When transferring money, it is usually instant due to they are all the banks being on the same network.
That feels unlikely since the Monzo card will force the transaction to be done online if at all possible. I guess a customer could live in a n area where no merchant supports online payments but it feels unlikely.
there’s some merchants that don’t take the money straight away even if you pay by card and even use chip and pin there’s a few shops i’ve been to that this happened