Our team would like to be transparent about the known issues found in this release, while investigation is going on and fixes are being implemented. If you encountered similar issues, please provide all necessary details to us for investigation (synchrosupport@bentley.com) In the meantime, please try out the provided workaround to see if the issues still persist. 

Shared geometry parts disappear after deleting certain 3D objects and reopening .sp file

The issue only occurs to certain 3D objects which contain shared geometry parts. To prevent unwanted geometry loss, use later Synchro 4D Pro versions where the issue is fixed: 6.5.4.35 or 6.5.5.28.