Problem is for the v11.0.0 related to the G4GeneralParticleSource, I think it is a bug. I made a post on this (https://geant4-forum.web.cern.ch/t/issue-using-gps-pos-confine-with-gdml-geometry/5734/2) but got no feedback (/cry).
Which version of Geant4 are you using? We haven't yet released version 11.0.
It seems you are using version 11.0-beta. Let me add the responsible of the G4PhysicalVolumeStore class in CC list for his comment.
Thanks for reporting the issue. The problem was due to a missing update of the volumes maps after the names stripping in GDML. The fix will be included in the final release.