If the Volumio device and the remote controllers (smartphone, tablet, etc..) are connected to 5GHz WiFi network, make sure the wifi range is optimal for any device.
Make sure only one connection among cable and WiFi is active. Multiple active connections, with different IP addresses, could create conflict on App recognition.
How to solve :
Boost WiFi network with an WiFi range extender OR put powerline extenders between Volumio device and the router if the unit is anyway out of wireless range
Switch all devices on 2.4GHz WiFi network. This connection has greater range.
Switch off the unused connection from NETWORK MENU
