refactor: Integrate encryption troubleshooting sections

Moved them all to the Encryption chapter rather than having them split between there and the general troubleshooting chapter.

And cleaned up some grammar and typos.

Signed-off-by: Josh <josh.t.richards@gmail.com>

admin_manual/configuration_files/encryption_configuration.rst

@@ -279,7 +279,7 @@ You can decrypt for individual users:
 Data Not Encrypted
 -------------------
 
-Only file contents is encrypted. The following are **not** encrypted:
+Only file contents are encrypted. The following are **not** encrypted:
 
 .. list-table::
    :header-rows: 1
@@ -328,9 +328,60 @@ LDAP and External User Backends
 Troubleshooting
 ---------------
 
-- **Invalid private key for encryption app:**
-  See `GitHub Issue #8546 <https://github.com/nextcloud/server/issues/8546>`_ and
-  `workaround <https://github.com/nextcloud/server/issues/8546#issuecomment-514139714>`_.
+Invalid private key for encryption app
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+See `GitHub Issue #8546 <https://github.com/nextcloud/server/issues/8546>`_ and
+`workaround <https://github.com/nextcloud/server/issues/8546#issuecomment-514139714>`_.
+
+Bad signature error
+^^^^^^^^^^^^^^^^^^^
+
+In some rare cases, encrypted files cannot be downloaded and return a "500 Internal Server Error." If the Nextcloud log contains an error about "Bad Signature," run the following command to repair affected files::
+
+   occ encryption:fix-encrypted-version userId --path=/path/to/broken/file.txt
+
+Replace "userId" and the path accordingly.
+The command will perform a test decryption for all files and automatically repair those with a signature error.
+
+.. _troubleshooting_encryption_key_not_found:
+
+Encryption key cannot be found
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If the logs contain an error stating that the encryption key cannot be found, you can manually search the data directory for a folder that has the same name as the file name.
+For example, if a file "example.md" cannot be decrypted, run::
+
+   find path/to/datadir -name example.md -type d
+
+Then check the results located in the ``files_encryption`` folder.
+If the key folder is in the wrong location, move it to the correct folder and try again.
+
+The ``data/files_encryption`` folder contains encryption keys for group folders and system-wide external storages,
+while ``data/$userid/files_encryption`` contains the keys for specific user storage files.
+
+.. note::
+
+   This can happen if encryption was disabled at some point but the :ref:`occ command for decrypt-all<occ_disable_encryption_label>` was not run.
+   If someone then moved the files to another location, the keys did not get moved.
+
+Encryption key cannot be found with external storage or group folders
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+To resolve this issue, run the following command::
+
+   sudo -E -u www-data php occ encryption:fix-key-location <user-id>
+
+This will attempt to recover keys that were not moved properly.
+
+If this doesn't resolve the problem, refer to the section :ref:`Encryption key cannot be found<troubleshooting_encryption_key_not_found>` for a manual procedure.
+
+.. note::
+
+   There were two known issues where:
+
+   - moving files between an encrypted and non-encrypted storage like external storage or group folder `would not move the keys with the files <https://github.com/nextcloud/groupfolders/issues/1896>`_.
+   - putting files on system-wide external storage would store the keys in the `wrong location <https://github.com/nextcloud/server/pull/32690>`_.
 
 Further Reading
 ---------------