Many web users were bothered by nuisance audio coming from web sites that automatically play when a page is loaded, such as that from videos and advertisements. To address this, Chrome and Safari browsers added a feature that blocks audio by default from web pages if the page or tab is refreshed, but not clicked on by the user.
Therefore, if you haven't accessed the MultiLine Desktop tab since the last time it refreshed (for example, if you closed and restarted chrome and loaded your tabs from the previous session) the ringing sound will be blocked. However, you'll still be able to see the visual notification of the incoming call.
To unblock the ringtone from being played, open the tab where MultiLine Desktop has recently refreshed and click anywhere within the MultiLine Desktop application and this should ensure that the ring sound will play.