Q: mac and mouse keep disconnecting and reconnecting

Restart the computer holding down the command - option/alt - P - R keys before the gray screen appears. Continue to hold until you hear the startup chime for the second time.

Reset NVRAM/PRAM

Try a SMC reset. The article covers when this is required, but doing this will not affect anything.

Reset SMC

Keyboard/Mouse – Troubleshooting Wireless

Reset an Apple Wireless Bluetooth Keyboard, Mouse or Trackpad (Troubleshooting Pairing and Other Common Problems)

Bluetooth devices become unresponsive

Bluetooth Interference Sources

Bluetooth Interference Sources (2)

Bluetooth Wireless Problems

If your Wi-Fi is capable of generating a 5 GHz signal, try that.

I have noticed this too since i just updated to 10.11.6

tried everything and also tried another magic mouse, but it still keeps happening from some reason??