As you can see, the G string getting out of tune can be caused by a million little different things. Nut slots friction, nut slot depth, nut action height, nut position, and so on. Also, there can be a bigger problem with your guitar. Bent neck, tuners loose, intonation problems, and so on.
Why is my G string always out of tune?
“The height of the G slot in the nut can really impact things,” Pullen explains. “If it is too high, that extra distance you need to press the string down to fret the note will bend it out of tune.” Additionally, the string gauge needs to be matched to the guitar's scale.