Simultaneously with the Event Horizon Telescope (EHT) imaging the black-hole shadow of M87 for the first time in 2017, an extensive multi-wavelength (MWL) observational campaign was conducted involving ground and space-based instruments covering fifteen decades of energy ranging from radio to very high-energy gamma rays. During this first campaign, the innermost knot HST-1 and the core of M87 were observed to be in historically low states. In 2018, a similar MWL observational campaign was carried out, during which we detected a brief gamma-ray flaring episode - the first gamma-ray flare observed in M87 in over a decade. We compare the results of the 2018 MWL campaign with the quiescent state observed the previous year along with a contemporaneous broad-band spectral energy distribution and MWL light curves. Additionally, heuristic modelling provides new insights into investigating the origin of the gamma-ray emission from M87.