  Recently, several studies reported a significant discrepancy between the
clustering and lensing of the Baryon Oscillation Spectroscopic Survey (BOSS)
galaxies in the $\textit{Planck}$ cosmology. We construct a simple yet powerful
model based on the linear theory to assess whether this discrepancy points
toward deviations from $\textit{Planck}$. Focusing on scales $10<R<30$
$h^{-1}\mathrm{Mpc}$, we model the amplitudes of clustering and lensing of BOSS
LOWZ galaxies using three parameters: galaxy bias $b_\mathrm{g}$, galaxy-matter
cross-correlation coefficient $r_\mathrm{gm}$, and $A$, defined as the ratio
between the true and $\textit{Planck}$ values of $\sigma_8$. Using the
cross-correlation matrix as a diagnostic, we detect systematic uncertainties
that drive spurious correlations among the low-mass galaxies. After building a
clean LOWZ sample with $r_\mathrm{gm}\sim1$, we derive a joint constraint of
$b_\mathrm{g}$ and $A$ from clustering+lensing, yielding
$b_\mathrm{g}=2.47_{-0.30}^{+0.36}$ and $A=0.81_{-0.09}^{+0.10}$, i.e., a
$2\sigma$ tension with $\textit{Planck}$. However, due to the strong degeneracy
between $b_\mathrm{g}$ and $A$, systematic uncertainties in $b_\mathrm{g}$
could masquerade as a tension with $A=1$. To ascertain this possibility, we
develop a new method to measure $b_\mathrm{g}$ from the cluster-galaxy
cross-correlation and cluster weak lensing using an overlapping cluster sample.
By applying the independent bias measurement ($b_\mathrm{g}=1.76\pm0.22$) as a
prior, we successfully break the degeneracy and derive stringent constraints of
$b_\mathrm{g}=2.02_{-0.15}^{+0.16}$ and $A=0.96\pm0.07$. Therefore, our result
suggests that the large-scale clustering and lensing of LOWZ galaxies are
consistent with $\textit{Planck}$, while the different bias estimates may be
related to some observational systematics in the target selection.
