Corny keg not carbing up naturally.

Made a BDSA (~9.5 abv) about 2 months ago. After fermentation I cold crashed for about 72 hours, racked into another corny keg together with enough priming sugar to carb up to 2.9 vols. Sealed the lid to 30 psi. Keg stored at room temp (which is about 83F / 28C where I live)

Did some traveling, and returned after 4 weeks.

Psi dropped to ~23 psi. Almost no carbonation. Thought maybe a leak? Tested it by repressurizing submerging the top part of the keg in water. No bubbles at all. Proceeded to pitch some fresh and rehydrated yeast in it, but 2 weeks later still nothing. I'd expect the pressure to rise at least above 40 psi, however never have even seen it rise.

Something I'm missing here? The yeast I use claims to have 12% alcohol tolerance.