  The forward-backward (FB) asymmetry of $b$ quarks in $e^+e^-$ collisions at
the Z pole measured at LEP, $A_{FB}^{0,b} = 0.0992\pm0.0016$, remains today the
electroweak precision observable with the largest disagreement (2.4$\sigma$)
with respect to the Standard Model prediction, $(A_{FB}^{0,b})_{_{\rm th}} =
0.1030 \pm 0.0002$. Beyond the dominant statistical uncertainties, QCD effects,
such as $b$-quark showering and hadronization, are the leading sources of
$A_{FB}^{0,b}$ systematic uncertainty, and have not been revised in the last
twenty years. We reassess the QCD uncertainties of the eight original
$A_{FB}^{0,b}$ LEP measurements, using modern parton shower PYTHIA-8 and
PYTHIA-8 + VINCIA simulations with nine different implementations of soft and
collinear radiation as well as of parton fragmentation. Our analysis, combined
with NNLO massive $b$-quark corrections independently computed recently,
indicates total propagated QCD uncertainties of $\sim$0.7% and $\sim$0.3% for
the lepton-charge and jet-charge analyses, respectively, that are about a
factor of two smaller than those of the original LEP results. Accounting for
such updated QCD effects leads to a new $A_{FB}^{0,b} = 0.0996\pm0.0016$
average, with a data-theory tension slightly reduced from 2.4$\sigma$ to
2.1$\sigma$. Confirmation or resolution of this long-term discrepancy requires
a new high-luminosity $e^+e^-$ collider collecting orders-of-magnitude more
data at the Z pole to significantly reduce the $A_{FB}^{0,b}$ statistical
uncertainties.
