Same thing sporadically happened on my 3861, that was purchased new from an AD back in 2021. I sold it within a year for a significant loss. Prior to that, my 1861 Speedmasters never had this issue of the watch stopping... although both my 1861 Speedies had a different demerit of running ~15 seconds fast every day.
You could send it back to the boutique, where they will send the watch to a service center. They may observe it for a period of time, open up the movement only to diagnose no defects and send it right back to you. Or they may open up the movement, work on it, and send it back to you... in either scenario, you'll be without your brand new watch for weeks or months, while it's in the custody of the service center.
Unlike a new luxury automobile purchase for a high-volume mass luxury car brand... in the case of a watch in Omega's price range for stainless steel models, the boutique isn't going to issue a "loaner" while your watch is in the shop for warranty work. You'll have just paid very good money, for zero utility of any product/service during the time it's gone for warranty work.
In either of the 2 Omega service center scenarios, ask yourself: "will you ever have peace of mind and enjoyment in your new watch, knowing it can happen again any time during the remaining warranty period? And you'll then be without your watch again, for several weeks?" For me - that just wasn't worth it, and decided to sell my 3861 Moonwatch without looking back. Same reasoning is why I still won't go near a 32xx movement Rolex and am continuing to stick with the older 313x movements for the near future. With all of the issues reported on watch forums around that new Rolex movement's tendency to just suddenly begin running slow 1 day, totally out of the blue, I just won't full enjoyment of a watch with the newer movement whilst harboring the knowledge/prejudice in my mind that there's an older model available featuring a movement that strong track record, and has been refined and improved on for a couple decades.
I saw in your other thread that you like the polished accents on the sapphire 3861 bracelet. Maybe consider a trade, to move back 1 generation and get a 1861 Speedmaster? Both the hesalite and the sapphire sandwich 1861 Speedy Pros have polished vertical accents on the bracelets. If you're still into the history, design, and romance of the Moonwatch (and don't mind a watch running fast every day or taking it to an independent watchmaker to get it regulated), a 1861 could be a viable path forward. You might even get some cash back from one of the high-volume trusted sellers on this forum, if you pursue a trade in that direction.
