I have a 2018 L-00 Standard that I purchased new in 2019. About a year ago, I started experiencing the same fret buzzing that you describe. The buzzing got worse when capoed at the 3rd fret or higher. I tried everything to fix it: new strings, adjust the truss rod, different gauge strings. replaced the original saddle (I installed abone saddle shortly after I purchased the guitar). Nothing worked.
Then I ran a 6" scale across the frets and found the 15th fret to be slightly high. I also thought that it was in the area where it didn't matter. This summer I took it to a luthier and he confirmed that the high fret was a problem. The actual fretboard was high in that area, so his recommendation was to pull the lower frets, level the fretboard and install new frets. I had him do the repair and the buzzing is gone.
Jeff