If your SM3 Slim Mechanical Backlit Bluetooth Keyboard (ST-KSM3LT-EN, ST-KSM3DK-EN) drops the connection or lags while you type, try these steps.

How to stop the SM3 from disconnecting

1. Charge the keyboard for at least 30 minutes with a USB-C cable, since a low battery causes lag and dropouts.
2. Move USB 3.0 drives and hubs away from the keyboard and its receiver, since these interfere with the 2.4 GHz band that wireless keyboards use.
3. On your computer, remove or forget the SM3 in the Bluetooth list, then pair the SM3 again fresh.
4. If you use the 2.4 GHz USB receiver, plug the receiver into a port close to the keyboard, ideally a direct port rather than a hub.
5. Test the keyboard in wired mode with a USB-C cable. If the keyboard is stable when wired, the cause is wireless interference or pairing.