Umesh Agashe tripped over this today. Admin#closeRegion which we used to use in branch-1 will cause damage in AMv2 cluster. Instead you need to call unassign – i.e. all cluster ops must go via the Master; no more going direct to RegionServer closing regions behind the Master's back.
Review all Admin ops to see what else skirts Master and deprecate and throw unsupported if called.