Which date is the backup you restored?
If you restored a backup that dates from before DuckDB ( Gladys Assistant 4.45 : DuckDB, une révolution dans Gladys ! ⚡ ), then your instance needs to redo the migration to DuckDB locally and then you’ll recover the historical data.
Otherwise, you can look at the restore logs and see if everything went well (check your Gladys logs, you should have it)
Another possibility: redo a restore and watch the logs live to verify that everything goes well 
Maybe there’s a particular case in your historical data that causes the restoration of those data to fail.
Are you using the MQTT integration via the Docker container launched by Gladys or one that you started manually?
You may need to restart the integration; normally it’s supposed to get back on its feet after a restore (the container should restart by itself if you use the container launched by Gladys), but maybe in your case it didn’t work.
Given everything you’re encountering, it’s possible that the restore failed in your case; the logs will tell us more about what happened