#1
Hey guys,
Hopefully someone can help me with this!
So I've manage to perfectly intonate my guitar but there is still an issue
Hitting 0 and 12 is fine, no issue, but I noticed that some of the strings are slightly flat on the 24th fret
I noticed this after playing certain chords.

Playing a standard 2 note D5 chord (D, 5th String 5th Fret. A 4th String 7th Fret) everything is fine, but when I move the A to a B (Sliding the 4 string up to fret 9) Everything is out of whack, yet I can play this chord perfectly up an octave still on the same strings

Could this possibly be a truss rod issue or something else?

Thanks!
#2
adjust your saddles. intonnate the same way you do at the 12th fret (preferably using harmonics) except do it at the 24th fret. the issue is that you havent intonnated your guitar precisely enough, itll be far more precise at the 24th
Youtube: Musishoon