What does a change from white to red indicator above the SD CARD indicate?

The white circle indicator just to the top right of the SD card is now red for my LG G4. Does anyone know what this indicates? I haven't exposed it to any water that I know of.

I've been having random problems with reboots especially when the phone is hot, charging, heavy use, etc. I want to send the device into warranty but I'd like to know what I am dealing with first.