No flat line when using "Mediaentity" backend with wavesurfer

Hi.

In have wavesurfer.js installed successfully. The waveform is generated and the playback works after the mp3 file is fully loaded.

I have read that I can use the "Mediaentity" backend inside wavesurfer settings to be able to play the file immediately. The flat line is supposed to be displayed until the waveform is loaded... but there is no flatline visible in my case and the play option is not available up until the whole mp3 is loaded... just like with default "Webaudio" backend option.

D10.1.6
Audiofield 8.x-1.13
Wavesurfer "version": "7.5.1",