Add broken instance data export to known issues

README.md

@@ -271,6 +271,9 @@ If you want to use a different user for the command line interface, you can gene
 - The `instance.auto_start` option is currently is broken and will not work, turn it off and do not use it for now.
 - When the `server_select` plugin is installed you may see `[error] Unhandled event server_select:UpdateInstancesEvent` logged when starting an instance.
   This should be ignored as it does not indicate an error occured.
+- After migrating from Alpha 13 to Alpha 14 running an instance data export fails with the error `Upload failed: 401 Unauthorized` due to the host token being issued to a slave.
+  To workaround this find the id of the host in the host config and generate a new host token with the same id.
+  Stop the host and replace the value of the `host.controller_token` field in `config-host.json` with the new host token before starting it up again.
 
 
 ## Common problems