LED strip forgets last setting when turned off
The controller needs to be continuously powered in order to remember the dimmer setting. Unfortunately, the electrician wired the timer so that it interrupts power to the controller.

One way to fix this would be to purchase a relay that has a 230V coil and contacts rated to handle the DC current at the output of the controller.

Wire the controller's AC input directly to the mains.

Wire the output of the timer to the relay coil.

Wire the relay contacts in series with the output of the controller (i.e., between the controller and the LED strip).