Krystal returns to 5-day working week (ends 4-day trial) (news.ycombinator.com)

"The hope was that the extra time off would reduce stress and make staff happier and more productive. Unfortunately, we found the opposite was true."

> We’re also hiring for 5 additional support staff to bolster the team by 20% (in addition to the 20% output we’re aiming to recover from going back to 5 days). I’m confident that support levels will be back to the usual levels you’ve come to know and expect in no time at all.

Sounds like that was a staff shortage issue.

That's why you see some companies offer 4 day week to their departments with creative roles and not task-oriented with easily measurable output such as warehouses, a good example is ThredUp company.