Koum confirmed his departure from WhatsApp on his Facebook page saying was time to “move on” but did not elaborate on his reason for leaving. To which Zuckerberg replied that would miss working with Koum.
Koum also plans to resign from Facebook’s board of directors according to Washington Post and may also have been embroiled in a rift with Facebook management over the Facebook-Cambridge Analytica data scandal which involved the collection of personal data of up to 87 million Facebook users. This data was allegedly used to attempt to influence voter opinion during the 2016 US Presidential elections.
(Source: Hindustan Times YouTube channel)