Apparently, some Samsung Galaxy S9+ devices have issues with their touchscreen where it doesn't register pressing. Not the whole screen is affected, but rather a small part of it surrounding the letters E, R, and T on the Gboard keyboard (you dig the intro now, don't you). Some users have also reported screen "dead" spots around the top or bottom bezels and near the edges of the Galaxy S9+. There've been some reports of the issue on the regular Galaxy S9, but they are much less than on the S9+.
We've listed down some user reports regarding the touchscreen issue below:
The touchscreen issues are most likely related to the hardware of the Galaxy S9+, although we've never seen a Galaxy flagship to have such problems. Those also are some of the first devices shipped, so the hardware will probably be fixed by the second "wave" of Galaxy S9+ devices.
The issue seems to plague a relatively small number of devices, but in case your Galaxy S9 / S9+ has a malfunctioning touchscreen don't hesitate to immediately visit the retailer or wireless operator you've bought it from and ask for a new device. Touchscreen problems are covered by your warranty, so no reason to hold on to a broken device.