Help: Can't rid of severe fret buzz after multiple repairs, looking for suggestions :(

Help: Can't rid of severe fret buzz after multiple repairs, looking for suggestions 🙁

Enlish is not my first language, so I aplogize in advance.
I own BFR MM SR5 all rosewood neck, which is my dream bass sound wise, but it has some serious issues I’m trying to resolve for several years already. The is significant buzz even at pretty high action.
I’ve bought it used and I got kind of scammed, because the bass fretboard was warped, but I did not know it until I went to a recommended luthier to set everything up properly.
He sanded down the fretboard, made a refret, but the buzz did not go away. The guy said he does not know why and rosewood neck is crap, blablabla. Fail #1
I tried to get over it since I was really in love with the instrument and it was not that bad for fingerstyle and chill and simple music like post-rock, but later I’ve made another attempt to fix it.
I started to play heavier music, a lot pick playing, so high action and buzz started to spoil the fun again.
I went to another recommended luthier 😀 This guy said the first guy was an idiot and did not sand the fb enough. So he sanded it again, did a refret, reajusted the neck pocket, glued in a new nut (EB guys were kind enough to send me a couple of those nice patented nuts, because mine was damaged during the 1st repair :D) and checked everything else.
The buzz did not go away and the guy said he does not know why. :rolleyes: Fail #2

Any ideas what else can I check? After 2 shaves fb surface is almost chewing fret markers. Action is about 3.5mm on B and 3mm on E, but the buzz is still pretty bad.
I’m thinking of replacing entire fretboard, but if it won’t help, idk what else can I do.

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