The touchscreen on your phone is the primary way you interact with it, so it absolutely needs to work. That makes problems like so-called "dead zones" or ignored/unregistered inputs among the most annoying out there. Based on reports, many are running into those types of touchscreen input problems with Samsung's Galaxy S9+.
It's tough to tell precisely how common the problem might be. Few users are as apt to report issues as Pixel-purchasers, so we can't quite compare things against our coverage for Google's hardware. But from what we have seen in places like Reddit, it's reasonably widespread.
We aren't sure why, but based on reports, the problem seems more prevalent with the bigger Galaxy S9+. While we have seen a couple of claims that name the smaller phone, it's the larger model that is most frequently referenced.
GIF of the issue recorded by Redditor bobdurfob
The problem manifests as you'd expect: a chunk of the touchscreen's digitizer just doesn't seem to work. Interestingly, not all users are reporting issues with the same physical areas of the display. For some, it's the top of the screen that isn't accepting input—resulting in an inability to pull down the notification tray—but for others, it's the bottom of the screen that's wonking out in the traditional keyboard input area.
A few people have been able to diminish the effect by cranking up the touchscreen sensitivity, and there's at least one report of a factory reset fixing things. But for many, the problem persists between wipes. Worse, some people with the problem have experienced further issues seeking help via Samsung's support process if a trade-in was involved.
If you were considering swapping some hardware for the S9+, it might be a good idea to wait on sending your old device in until you're sure your new unit doesn't have any problems. Or you can just sell your old hardware on eBay or Swappa for more money. After all, Samsung's pretty well known for the monumental disaster last year's trade-ins were.
Alternate title: Samsung's Galaxy S9 rejects your love, your touch
Samsung has released a statement concerning these reports. Given how hardware failures of a flagship handset must be a bit of a touchy subject for the manufacturer, it's good to see some acknowledgement of the problem, even if there's not much new insight here just yet:
At Samsung, customer satisfaction is core to our business and we aim to deliver the best possible experience. We are looking into a limited number of reports of Galaxy S9/S9+ touchscreen responsiveness issues. We are working with affected customers and investigating. We encourage any customer with questions to contact us directly at 1-800-SAMSUNG.