  Measurements of $b \rightarrow s \mu^+ \mu^-$ transitions indicate that there
may be a new physics field coupling to di-muon pairs associated with the $b$ to
$s$ flavour transition. Including the 2022 LHCb reanalysis of $R_K$ and
$R_{K^\ast}$, one infers that there may also be associated new physics in
$b\rightarrow e^+ e^-$ transitions. Here, we examine the extent of the
statistical preference for $Z^\prime$ models coupling to di-electron pairs
taking into account the relevant constraints, in particular from experiments at
LEP-2. We identify an anomaly-free set of models which interpolates between the
$Z^\prime$ not coupling to electrons at all, to one in which there is an equal
$Z^\prime$ coupling to muons and electrons (but where in all models in the set,
the $Z^\prime$ boson can mediate $b\rightarrow \mu^+ \mu^-$ transitions). A
$3B_3-L_e-2L_\mu$ model provides a close-to-optimal fit to the pertinent
measurements along the line of interpolation. We have (re-)calculated
predictions for the relevant LEP-2 observables in terms of dimension-6 SMEFT
operators and put them into the ${\tt flavio2.3.3}$ computer program, so that
they are available for global fits.
