HC-05 bluetooth module
The HC-05 modules use bluetooth 2.0. Certain apps would only be compatible with bluetooth 4.0 devices (BLE - Bluetooth Low Energy), such as an HM10 or AT09. 

It could be that your app requires the device to use v4.0+. Are you able to find, and pair with the device using your android's default bluetooth device scanning/pairing features? 

Assuming that your app does not require v4.0+, have you removed the connection from 'en'/'ch_pd' to 3.3v? If that was still connected (which is a required connection to enter AT command mode), then your bt module would not be able to accept incoming pair requests etc. 

hope this has helped. :)