  In view of the latest experimental results recently released by the ATOMKI
collaboration, we critically re-examine the possible theoretical interpretation
of the observed anomalies in terms of a new BSM boson $X$ with mass
$\sim17\;$MeV. To this end we employ a multipole expansion method and give an
estimate for the range of values of the nucleon couplings to the new light
state in order to match the experimental observations. Our conclusions identify
the axial vector state as the most promising candidate, while other spin/parity
assignments seems disfavored for a combined explanation. This results is
however based on an order of magnitude estimate for the, currently unknown,
axial nuclear matrix element of the $^{12}$C transition, that needs then to be
evaluated before being able to draw a definite conclusion. Intriguingly, an
axial vector state can also simultaneously accommodate other experimental
anomalies, {\emph{i.e.}} the KTeV anomaly in $\pi^0 \to e^+ e^-$ decay while
being compatible with the conflicting measurements of the anomalous magnetic
moment of the electron $(g-2)_e$ and other constraints on the electron
couplings of the $X$ boson. The PADME experiment will completely cover the
relevant region of the parameter space, thus allowing for a strong test of the
existence of the $X$ particle.
