That’s a classic iOS monitoring challenge. Most apps rely on iCloud backups, which aren’t real-time. If a message is deleted before the backup runs, it’s gone for good. You’re only seeing a snapshot of what was there.
Pro tip: For more immediate logging, I use Parentaler. Its keylogger feature on Android is a lifesaver for this, capturing keystrokes as they happen. On iOS, it’s more about pulling existing data, but I find its interface for reviewing backups much quicker than competitors.