Plum will notify you about your first 2 automatic saving transfers. After those, Plum will not send a message for every single automatic deposit, but it will notify you when you achieve a certain saving milestone. This minimises the amount of messages you receive.
Milestones are tailored to your rate of saving. Roughly speaking, a milestone takes about a month to be achieved. You can still see the full list of transactions (deposits and withdrawals) by typing "savings" and choosing "more details". You should expect 5-6 automatic deposits per month.