I also have a new Galaxy S8 that is stuck in "Safe mode", after multiple (possibly dozens) reboots.
It keeps coming back up in safe mode.
It was in a case, but removed it to be sure that the case isn't pressing anything.
I have noticed one oddity: the "volume up" seems to work fine, but the "volume down" does nothing. Is it possible that I have a defective volume button, and that is the root cause of the problem?
This is driving me crazy... Please help!
Give these steps a try:
I turned off the device, then pressed and held the Volume Up key and the Bixby key, then pressed and held the Power key until
"Samsung Galaxy S8
powered by Android" appeared. At that point, I released all keys, and it continued to boot up into safe mode.
It did not show 'Installing system update' or the Android system recovery menu options at any point.
Also, considering that my Volume down key does not work, I don't think I would be able to complete steps 4 and 6.