@scottiespike: Sorry to hear that you're having some issues getting a stable mobile network signal on your Galaxy A40. Is the issue persistent everywhere, or is it only occurring in certain locations? Have you recently started using a case or cover on the phone that might be obstructing the antenna?
I'd certainly recommend reaching out to your network provider directly, as they may be carrying out some maintenance in your area which is causing your signal to drop? Typically they will text you to advise of this, but it is worth exploring as an option. If you haven't already done so, please restart your A40 by pressing and holding the Power key on the side of the device, and selecting Restart from the Power menu that appears on screen. This will refresh the software, and address any temporary issues that might be affecting the performance of the phone. You can also try heading to the Samsung Members app > Press and hold on the app icon > Diagnostics > Mobile network, to see if this flags any issues.