Check your MB specs for the total current permitted on the USB connection(s). Total the current requirements for each of the devices plugged into the USB connection(s), which is specified in the documentation for each device that requires power. If the total exceeds the power available, move some devices to another (independently powered) hub.
While I've found fixes in several distributions for this, it doesn't look like anyone has reported the bug for Gentoo. Perhaps as a user of that distribution you should report it so it gets addressed: