According to a Redditor, there is a bug with some S8/S8+ phones where they will not let you know the battery is getting low and then subsequently die while plugged in to the Gear VR. After that, they go into a bootloop instead of charging, unless you try to turn it on first and then plug it in.
Not having an S8 phone and not having seen any official reports, I cannot verify this, but just FYI if you have an S8, don't let it die while in VR. Make use of the charging port on the Gear VR itself if you need to. ;-)
Warning: DO NOT let phone die while in new Gear VR!