Unphysical properties in a class of interacting dark energy models R. von Marttens, H. A. Borges, S. Carneiro, J. S. Alcaniz and W. Zimdahl Eur. Phys. J. C, 80 12 (2020) 1110 Published online: 03 December 2020 DOI: 10.1140/epjc/s10052-020-08682-5