Two years ago, Salesforce co-founder and CEO Marc Benioff gushed about his software company’s $28 billion purchase of messaging app Slack, describing it as a “match made in heaven.” It was also the most expensive subscription software acquisition of all time, with Salesforce paying around 26 times Slack’s forward revenue—a price tag that carried high expectations.

But problems emerged from the start. Mutual distrust between Benioff and Slack CEO Stewart Butterfield became a distraction, according to more than a half-dozen current and former employees with direct knowledge of the situation. Before the deal was even consummated, Benioff went out of his way to distance himself from Slack in public and private conversations, repeatedly telling colleagues and outside observers that Bret Taylor, who was then president and chief operating officer at Salesforce, was the deal’s architect. Senior Salesforce staff were skeptical that they could increase sales by bundling and integrating Slack with its other products—a core rationale for the acquisition.