i couldn't find my device on nrf connect toolbox

hello , friends 

i am using nrf52832 ,debugged the ble uart program ,and then i tried to connect  my device over ble uart app,i couldn't  found my device ,then i tried to connect  my ble device in four different  phone at different  time ,finally i connect  my ble device.    out of four phones , in one only i can able to connect .why ?

i am crossing this issue at several times .i dono why it happen?