Samsung has recently brought its dedicated camera night mode to the Galaxy S9 family and the Note9, but for these devices unfortunately it's not all smooth sailing. Some frustrated owners have taken to online forums such as XDA-Developers to vent about the camera app crashing and not saving pictures taken in this mode. The app just throws a "camera failed" warning at the user and calls it a day (or night, as would be more fitting in this case).
To be perfectly clear, this doesn't seem to affect every S9 or Note9 owner, and not all people are affected in the same way. Some report the camera app failing to take a night mode shot more than 90% of the time, while for others it's happening far less frequently.
A possible temporary fix seems to be setting the aspect ratio for the photos to 16:9 instead of the default 4:3, but you may not want your shots to come out in that way - and you'll also lose resolution in the process as 16:9 images are 9.1 MP compared to 12 MP for 4:3.
Hopefully Samsung will get to the bottom of this soon and issue an update that fixes the crashes. At the moment no reason for this weird behavior has been discovered, but the "camera failed" error does appear to be easier to trigger if you don't hold your device perfectly still while capturing a night mode photo - or even if the things you are shooting are moving. Such situations would result in blurry images because of how the night mode works, but every other phone with this feature simply saves those instead of resorting to such error messages.
I am not able take night mode shots in power save mode. Normal mode no crashes.
I experience the same and reported it already. I thought that I was just among the "few" unfortunate ones, but it turned out that others also experience the same.