Do you have auto-unlock enabled on your phone? Auto-unlock will unlock whenever its criteria are met, which are 1. you triggered the geofence around your Sesame and got the "Welcome back" notification and 2. your phone was able to connect to Sesame. It does NOT take into consideration whether the Sesame has been unlocked before these two things happened - it doesn't pay attention to whether the door was recently unlocked or not.
One way to get around this is to turn off auto-unlock entirely, but this would not be ideal if you do want it to trigger sometimes. If you want to keep auto-unlock enabled but don't want it to trigger every time, one thing you can do is to open the Sesame app when you DO NOT want auto-unlock to trigger. Launching the app, whether by clicking on the app icon or clicking on the "Welcome back" notification, will terminate the auto-unlock process for that specific instance without disabling auto-unlock permanently. So if you want to use auto-unlock most days rather than turn it off and just use your Apple watch or keys, you can leave auto-unlock enabled, and just launch the app on the days when you don't want to the door to auto-unlock.
Hope this information helps! - CANDY HOUSE