This had been my experience too. I don't think I had been more productive - many times I've just stayed late poking at the problem I'd normally leave for the next day when working in the office. Most of these times I still solved it the next day with the new ideas after a night's sleep. Not to mention I've got many ideas from random discussions with colleagues, which ceased with the WFH. So return to the office is a win-win for me and my employer: I work less and I am more productive.