Neutrino mass generation is needed to explain neutrino oscillations. Several new physics models, such as left-right symmetric models or seesaw mechanisms, offer a solution and motivate searches for heavy bosons or heavy neutral leptons in either opposite-charge or same-charge leptons final states. This contribution discusses the challenging backgrounds for same-charge final states, either due to jets incorrectly identified as leptons or due to mismeasurements of the electron charge. The results presented here use the data collected by the ATLAS experiment at the LHC with a center-of-mass energy of $\sqrt{s}=13$ TeV.