I have a clear enclosure with a mix of different isopods, and I've noticed some of the armadillidium, especially nasatum, seem to occasionally get their front half stuck in shed and die. I've tried reducing humidity, and upping it. I'm currently watching one, through foggy plastic, that appears to be stuck. I've also tried increasing calcium with egg shells (although I believe I overdid it at one point and had a few die off so I haven't added any for few months now). I make sure to have protein sources available constantly through fish/dog/cat food (that's removed if it begins to mold) plus nutritional yeast (mostly for the springtails but the isopods enjoy running off with the flakes)
Maybe the more aggressive species are keeping the rolys from the dampest areas? But I don't really see them picking on each other across species..