Log message content in C++ when sending notification. Do this for every message type. Additionally temporarily modify send.js prepareAndroidNotification code to send notification as if codeVersion < 31 and check that messages are still parsed correctly.
Comment out set_encryption_key method in SQLiteQueryExecutor (to disable encryption) code build app on an emulator, launch it and immediately kill. Then send a message from another client. Open device file explorer in Android studio and download comm.sqlite database. Examine its content in some sqlite explorer (vscode has a preety good one) to ensure that messages are there even though app was not launched after sending message.