A couple of weeks ago I filled it up and the fuel level on the RID was one bar down from where it usually is, then after a few miles it went back up. Now it's stays at one bar down when full. Has anyone else experienced this and is there a fix?
You could try taking the fuel tank off, uncoupling the block connector which is on the right hand side and giving the contacts a good clean. I had this once, and a clean of the pins with a dremel solved it. You need a very thin bit to get inside the female half but once done mine didn't give me any further issues.
Has the bike been serviced recently? If the plate on the tank where the fuel level sender sits isn't mounted in the right position it can give funny readings. It would have to exactly coincide with you noticing the issue though.
Hope it's a quick fix then. But if not it's not such a problem, my 1200 suffers the fuel gauge issue so I just ignore it and use the trip meter on the sat nav and on the bike to tell me when I need fuel. Re set both of them at each fuel stop and I know then when need to stop again. Annoying at first but soon get used to it.