3cx live chat WP button Greyed only in mobile responsive mode

[maxz]

I have a WP responsive website, in desktop mode the 3cx icon LiveChat works well, in mobile mode it appears gray (disabled)

 

[maxz]

i've removed and re-applied the plugin on my test page, now the widget works well in responsive mobile mode
i try to test it in the next days, using different browser (edge, chrome, etc.)