The paper presents Mössbauer spectroscopy investigation on superconducting Rb0.8Fe1.6Se2 exhibiting nanoscale phase separation and two its derivatives: Cu-doped Rb_0.8Fe_1.56Cu_0.04Se₂and Fe-deficient Rb_0.7Fe_1.4Se₂. The spectra reveal the presence of the same dominant magnetic sextet in the samples, which is assigned to the Fe 16i sites of the √ 5 × √ 5 × 1 superstructure. This magnetic part is independent on the modification of the sample and does not undergo any changes after doping or deviation of stoichiometry. In contrast, the minor non-magnetic doublet in the spectra of Rb_0.8Fe_1.6Se₂, which is attributed to the superconducting nanoscale phase, is sensitive to such modifications. After doping with Cu, the relative intensity of non-magnetic doublet significantly decreases together with suppression of superconductivity. On the other hand, the Fe-deficient sample is entirely magnetically ordered below 250 K including in the minor nanoscale phase. A discussion of Mössbauer spectroscopic data and comparison with previous studies on other Fe chalcogenide analogues allow to conclude the nanosized phase separation is also observed in non-stoichiometric and doped modifications of Rb_0.8Fe_1.6Se₂.