Unphysical properties in a class of interacting dark energy modelsR. von Marttens, H. A. Borges, S. Carneiro, J. S. Alcaniz and W. ZimdahlEur. Phys. J. C, 80 12 (2020) 1110DOI: https://doi.org/10.1140/epjc/s10052-020-08682-5