  PKS 1830$-$211 is a $\gamma$-ray emitting, high-redshift (z $= 2.507 \pm
0.002$), lensed flat-spectrum radio quasar. During the period mid-February to
mid-April 2019, this source underwent a series of strong $\gamma$-ray flares
that were detected by both AGILE-GRID and Fermi-LAT, reaching a maximum
$\gamma$-ray flux of $F_{\rm E>100 MeV}\approx 2.3\times10^{-5}$ ph cm$^{-2}$
s$^{-1}$. Here we report on a coordinated campaign from both on-ground
(Medicina, OVRO, REM, SRT) and orbiting facilities (AGILE, Fermi, INTEGRAL,
NuSTAR, Swift, Chandra), with the aim of investigating the multi-wavelength
properties of PKS 1830$-$211 through nearly simultaneous observations presented
here for the first time. We find a possible break in the radio spectra in
different epochs above 15 GHz, and a clear maximum of the 15 GHz data
approximately 110 days after the $\gamma$-ray main activity periods. The
spectral energy distribution shows a very pronounced Compton dominance (> 200)
which challenges the canonical one-component emission model. Therefore we
propose that the cooled electrons of the first component are re-accelerated to
a second component by, e.g., kink or tearing instability during the
$\gamma$-ray flaring periods. We also note that PKS 1830$-$211 could be a
promising candidate for future observations with both Compton satellites (e.g.,
e-ASTROGAM) and Cherenkov arrays (CTAO) which will help, thanks to their
improved sensitivity, in extending the data availability in energy bands
currently uncovered.
