** Unable to decrypt message each time app is opened

Each time I get a "Message" notification, I open up the Element app and the message is unable to be decrypted. After a few minutes of messaging back and forth, all messages suddenly become visible. Why is this?

There is only one session, and is verified by both of us in the chat room. When we finish messaging, I close the app (without logging out). When I get a new message push notification after a while, I open the app, and it's unable to be decrypted again - same process all over again.