All that trouble of adjusting the neck and the bridge was for naught! BooHoo!
The brand new Rotosound lights' D string seemed to have had a tiny little kink in it around the seventh fret location (mine is fretless).
I restrung the D with an older string and the buzz vanished!
"F"!
Or in this case: "D", or "G"-string! haha! So full of myself! Pardon.
Anyway, I restored the neck tension(s) - tightened 'em back up - and lowered the action to my usual razor thin margins.
She sings again like a birdie!
Need to add a topic in the 'club' that strings can be kinky! LOL!
And when they own up to their "kink", they will f-ing drive you nuts!
No pun intended - or - well a tiny kinky pun night be intended!
The first time in many years that I've encountered a rouge string in such a particularly weird place.
It was a perfect storm to trip up on such a gnarely string buzz on my 'precious'!
DISCLAIMER: the topic is related to FRETLESS!
Fretted -uh- units, will likey forgive tiny kinks, like we all should in real life, socially, anyway!

But, what with the pan-demonium - "cough" I am practicing, daily, quadruple durations now
And well, this hiccup had me freaking @220 BPM w/64th quintuplet notes . . . Ha!
Stay safe me' droogs: Girls and Boyz!
See you on the other side . . . 🎻