Ihkbird IBS PO1/B

I have bought myself the inkbird IBS PO1/B and have set it up ok. It works with the bluetooth.
I have the bluetooth on my phone on all the time…so why is it that after using the app and then re-check later it takes the app a while to re-connect and run again.
Is there anway to have the app set up so it is always running ? Doesn’t seem to be anything in the settings option.