If you have an issue with encryption please read this!
discourse.joplinapp.org
May I suggest you build in a feature to notify people about this. So if this happens in the future, you will be able to notify people about this. This caused me a lot of trouble...

Encryption was recently upgrade to use AES-256 so any app you upgrade will start using this. The problem is that apps you do not upgrade will see these encrypted notes, and will not know how to decrypt them. That will result in encryption-related errors such as a Unknown decryption method.

  • First, there is no risk for your data. It cannot currently decrypted but it still there and it is not corrupted

  • To ensure you can decrypt those notes, make sure you update all your apps. If you did so, and it still doesn’t work double-check your version number. It should be:

    • Desktop: 2.11.11
    • Android: 2.11.1
    • iOS: 12.11.5
    • CLI: 2.11.1

  • All the official releases are up-to-date however some non-official channels have not updated their releases. In that case, contact the developer for that channel, or directly install our official release.

  • Once you start the upgraded version there may be some items that need to be manually processed for decryption. To do so, in the desktop app, go to Help => Sync status and click on “Retry all”. In the mobile app, go to to the configuration screen, scroll down to the “Sync status” button, then press “Retry all”.

Any question, feel free to ask here!