How come this sometimes work and sometimes it doesn’t?
Remote web interface by just accessing the account through myvolumio.org
You need fast internet at both ends, especially if you wish to listen to large, lossless audio files without stutter.
You obviously have to be outside the network that your Volumio is connected to when you access myvolumio.org remotely. You can test on your phone by disconnecting from wifi and using 4/5G.