Hard to say what could be wrong, but in many Android headunits the Bluetooth stack is broken. See this FAQ:
Problems with Android headunits - General / Frequently Asked Questions - RealDash Forum
I don’t know if this is a case with your device, but you could try with high quality USB OBD2 adapter instead of Bluetooth:
What Adapter shoud I use? - Connectivity / OBD2 - RealDash Forum