A nested union definition that worked ok in root5 is now in root6 not found any more.
Minimal example with the rootcint output is in the attachments. When running the command
rootcint -v4 -cint -f NestedClassOff.Dict.cc -c -I$ROOTSYS/include/root -p -I. NestedClassOff.h NestedClassOff.LinkDef.h
I get at the end this message
Error in <CloseStreamerInfoROOTFile>: Cannot find class FdUtil::Fd::_PixelNumber.
although clearly it seems the identifier is found several times.