Uber shut down a party at a satellite California office and at least one employee resigned after some celebrations marking its initial public offering last week got out of hand, according to current and former employees, a setback for the company’s efforts to change its corporate culture.

Those people said that the celebrations, which kicked off with company-provided mimosas on the day of one of the largest public offerings in recent history, made them feel uncomfortable and seemed immature — especially as Uber’s stock price plunged, erasing billions of dollars of value. It also reminded some of a more toxic company culture Uber has been striving to erase, causing something of a hangover.

“Old Uber hid themselves until today apparently,” said one employee, who spoke on the condition of anonymity because that person was not authorized to speak publicly.