  Measurements of the branching ratios of $B \to D^{(*)}\tau\bar\nu/B \to
D^{(*)}\ell\bar\nu$ and $B_c\to J/\psi\, \tau\bar\nu/B_c\to J/\psi\,
\ell\bar\nu$ by the BaBar, Belle and LHCb collaborations consistently point
towards an abundance of taus compared to channels with light leptons. However,
the ratio $\Lambda_b \to\Lambda_c \tau\bar\nu/\Lambda_b \to\Lambda_c
\ell\bar\nu$ shows a relative deficit in taus. In this paper, we critically
address whether data still points towards a coherent pattern of deviations, in
particular in light of the sum rule relating these decays in a
model-independent way. We find that no common new physics explanation of all
ratios is possible (within $2\sigma$ or $1.5\sigma$, depending on the ${\cal
R}(\Lambda_c)$ normalization to light lepton channels). While this
inconsistency could be a statistical fluctuation, further measurements are
required in order to converge to a coherent pattern of experimental results.
