I'd like to send a bug report to the developer, but I'm not sure where to write it. So write it here.
The value of [SETTINGS] - [VIDEO] - [DISPLAY] - [Gamma] will not be saved when the game ends. It is reset to 2.2 at next game startup.
Change [mouse right click] set to [SETTINGS] - [BINDS] - [Aim Down Sights (Hold)] to [Aim Down Sights (Toggle)] and start game play. Then the [mouse right click] binding set to [Spectate Previous Player] is deleted without permission.