The blazars B2 1811+31 and GB6 J1058+2817 were found to be in flaring state during 2020 and
2021, respectively. The high states of the sources were registered by the Fermi-LAT at energies
below 100 GeV, triggering observations at higher energies with the MAGIC telescopes, in the
UV/X rays with the Swift satellite and with ground-based radio and optical telescopes. The
observations in the very-high-energy (VHE, 100 GeV < E < 100 TeV) gamma-ray band led to
the first detection of both sources in this energy range. A long-term gamma-ray lightcurve was
derived using Fermi-LAT data, identifying the time intervals in which the two sources persisted
in a quiet state. Archival data collected in the radio to X-ray wavelengths showed that the two
sources exhibited intermediate-synchrotron-peaked BL Lac behaviors in their low states, rather
rare sources in the TeV sky. The high state of the two sources was deeply investigated thanks to the
coverage provided by multi-wavelength (MWL) observational campaigns. In this contribution,
we present the results of the gamma-ray observations which are included in a MWL observational
campaign organized on these sources during their high-states. We discuss the flare spectral
properties and temporal variability. In the high-energy gamma band, sub-daily-scale variability
and strong spectral hardening give evidence for compact emission regions responsible for the
radiative output at high energies during the flare.