Continuing the discussion from Create hollow solid from revolved curve:
Wirecut fails on a hollow object created with NonManifoldMerge and CreateRegions, adding an oversize cut plane to the inner surface and leaving it disconnected from the outer.
CreateRegionsWirecutBug.3dm (161.7 KB)
Workaround is to use boolean difference instead and cut the unwanted part of the polysurface away leaving the solid remainder properly closed.