  The cosmological parameters prefered by the cosmic microwave background (CMB)
primary anisotropies predict many more galaxy clusters than those that have
been detected via the thermal Sunyaev-Zeldovich (tSZ) effect. This tension has
attracted considerable attention since it could be evidence of physics beyond
the simplest $\Lambda$CDM model. However, an accurate and robust calibration of
the mass-observable relation for clusters is necessary for the comparison,
which has been proven difficult to obtain so far. Here, we present new
contraints on the mass-pressure relation by combining tSZ and CMB lensing
measurements about optically-selected clusters. Consequently, our galaxy
cluster sample is independent from the data employed to derive cosmological
constrains. We estimate an average hydrostatic mass bias of $b = 0.26 \pm
0.07$, with no significant mass nor redshift evolution. This value greatly
reduces the tension between the predictions of $\Lambda$CDM and the observed
abundance of tSZ clusters while being in agreement with recent estimations from
tSZ clustering. On the other hand, our value for $b$ is higher than the
predictions from hydro-dynamical simulations. This suggests the existence of
mechanisms driving large departures from hydrostatic equilibrium and that are
not included in state-of-the-art simulations, and/or unaccounted systematic
errors such as biases in the cluster catalogue due to the optical selection.
