Magnetic frustration and paramagnetic state transport anomalies in Ho4RhAl and Er4RhAl: Possible test cases for newly identified roles of itinerant electrons

•Complex antiferromagnetism and spin glass anomalies in Ho4RhAl and Er4RhAl.•Kondo-like electrical and magnetotransport anomalies in the paramagnetic state.•Negligible drop of spin-disorder contribution to resistivity below Néel temperature.•Magnetic and transport properties mimic those of exotic skyrmion Gd2PdSi3.•Test cases for theories predicting new roles of itinerant electrons and RKKY frustration.