Currently, after GC the survivor regions are not part of young gen cset group because we clear them from there when preparing for the next mutator phase.

I.e. the young gen cset group does not contain a reference to them, but the regions themselves still have it.

Apart from an issue during full gc where we need to uninstall their cset group references manually (instead of being handled while abandoning the young gen cset group) I do not think there is an issue.

The suspicious code has been introduced by JDK-8343782, but I think JDK-8336086 already had that issue but it was less explicit.