MWL lightcurve of B2 1811+31 in HE γ-rays (weekly binned Fermi-LAT data, upper panel) and optical R-band (instruments are reported in the legend, lower panel) in a period of around 250 days surrounding the October 2020 high state. This period corresponds approximately to the ‘Flare’ period (Table 2). In the upper panel, the solid red lines show the double-exponential fit (Eq. (5)) of the rising and falling trends in the Fermi-LAT lightcurve (Section 3.1.2).