Several days ago, my 2.4G mouse is broken because the usb receiver can not work properly, so I bought another bluetooth/2.4G mouse on taobao, which costs me only 30 yuan(5 dollars).But there is a small problem with the bluetooth connection.Sometimes the connection just dies and I can not reconnect it. I googled a lot and tried several ways, including

service bluetooth restart
systemctl restart bluetooth
rfkill block bluetooth
rfkill unblock bluetooth
bluetoothctl

But none of the above worked.

Finally, I found this page and edited one line of my grub file from

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

to

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash btusb.enable_autosuspend=0"

then execute

update-grub && reboot

Untill Now the mouse works fine.I hope this is "the solution".If anything goes wrong, I might update this info.

Hope this information can help someone.