Samsung 10 won't read Libre sensor initially

I've been using the Libre for about 2 months now. My Samsung 10 won't read new sensors so I have to start them off with the reader that the hospital provided me with. After that, the phone has no problems reading the sensor. The problem is that I can't get alarms on my phone and the other day I had a massive hypo whilst minding my granddaughter - all was well as my son came in shortly afterwards and so she was fine, but it was very scary as I had none of the normal symptoms of a hypo. If I had alarms on my phone, this wouldn't have happened. Can anyone suggest why the phone refuses to read new sensors please?