Lizaan

I have a Fuji XT3 and haven't used it for approximately 2 months, I switched it on and noticed that some of the settings I've changed defaulted back to factory settings, saying this, when I changed the settings to what I had it on, I realised the ISO is stuck on 800, if I dial down it goes to 51200, if I dial up it goes to 1600, 3200 etc. Its almost as if it makes a full 360 dial. So, I have no idea why my ISO is stuck on 800. Please can someone help me?