I have a John Lewis credit card added as an external account. The transaction dates Monzo displays don’t match those that the John Lewis app displays. E.g. I made a purchase on Thursday and the John Lewis app shows it as Thursday but Monzo shows it as Friday (I’m guessing that was when the purchase was actually processed). Another one appeared about 4 days later in Monzo (due to a weekend).
It would be useful to use the original transaction date as then the data in Monzo would match that in the John Lewis app, and also using the processed date messes with trends as a purchase I make at the end of one month can fall in to next month’s budget.