Hi @abarbar, thanks.
While the solver itself should now always be stable and not prone to energy explosions like the old Kangaroo, there are some specific types of geometric goals which can still cause runaway reactions, one being the isothermic goal. As I was mentioning in the linked thread - if the angles of the quads deform too far beyond some threshold this runaway effect can happen. There is then a grasshopper bug that if any point travels extremely far from the origin, the viewport stops showing grasshopper geometry altogether. If you reset your Kangaroo simulation and viewports(by clicking the 4 viewports icon) it should return though.