This is six months old and slowly all isopods and millipedes have died one by one. Why is this? Can I expect a resurgence?

They have food, oxygen, moisture, space, "caves" from a rocky-dirty shale substrate, the plants are absolutely thriving, so why have they gone? In what circumstances would they lay eggs perhaps? I have not opened the jar for about 4 months. (sorry for the blurriness I have yet to wipe down the inside)