It sounds like you either have Auto-Stash or Smart-Save turned on.

Auto-Stash is Stash’s automatic investment tool. It runs on a set schedule, so head to the app and adjust the timing or turn off Auto-Stash if you’d like to stop automatic deposits/investments.

Smart-Save is Stash’s innovative saving feature. It automatically takes small amounts of money from your linked checking account each day when you have the cash to spare. It keeps track of your spending patterns so we’ll never initiate a transfer when your balance is low. You can turn off Smart-Save from inside the Stash app or adjust the minimum bank balance so it doesn’t pull unless you have a minimum balance amount in your linked account.