This does not seem to be true anymore. Farming those areas gave me 5 "Light Mutated Material", 14 "Magic Stone S", 9 "Naturally Pink Water" and 8 "Odd Miasma Wood", but 0 Resistones.
In base game, as well as CN and 3in1 mods, the material can be obtained from locations Sewer, Renegade Hideout, and Underbase
The spawn however isn't guaranteed, it's randomized so even if you spend a day or three farming the locations you may still miss out on it...forgot what specific materials it was, but I recall on several playthroughs that it took me an in-game week of going through all stages until I actually managed to obtain some of the mats needed for the stuff I wanted to craft