It seems Kagi Assistant for Android is ignoring the fact that the keyboard is open and instead of closing the keyboard on the back swipe, the entire app closes. This seems to be. A common issue with Flutter, and could have something to do with the predictive back (i.e. you can peek at the previous screen and decide if you really want to back).
Back swipe on the right side should close the keyboard, not the entire app if the keyboard is open.