Keyboard and Mouse

When I separately pair a blue-tooth (BT) keyboard to my iPads, they work fine. When I separately pair a BT mouse to my iPads, they work fine. When I try to pair them both to my iPads, the following keys on the keyboard stops working; 7 8 9 u i o j k l m , . This anomaly has been confirmed with three different BT keyboards, two different BT mice and on two different iPads (a mini and a 12.9" pro) both running iOs 13.1.2.