I would like to bring up something that happened to someone I know during WhatsApp call. Person A was in US and person B in India and were audio calling through Whastapp on something work related. Person A starts hearing someone else on his side, nothing unexpected on Bs side. A started a new call and everything was fine. A said it reminded him of the crosstalk that was common during the landline days. Could it be a bug or was someone listening and forgot to turn off their mic? No idea.