1) Due to previous instance clones, sys_properties can be preserved, missed sys_class_name on sys_metadata.
2) There are few tables which were reparented from sys_metadata in NY and Orlando release one such example is "sys_hub_flow_component".
3) Orlando has new reparenting method called live reparenting which creates new like tables and copies the data.
4) Here the scenario is Deparenting, sys_hub_flow_component deparented from sys_metadata.
5) While copying the chunks into new tables, it does copy with query as "sys_class_name NOT IN" which excludes null values too.
So, it left the properties which doesn't have class names as orphans.
pbrun -p snow mysql-query *instanceName* --no-vertical "select sp.sys_id,sp.name,sm.sys_class_name,sm.sys_update_name from sys_properties sp left join sys_metadata sm on sp.sys_id=sm.sys_id where sm.sys_class_name is null or sm.sys_id is null"
Note: orphan properties are on sys_properties but do not exist on sys_metadata/
Before upgrade: Though sys_class_name made empty by clone we still have the property in the proper accessible state so before the upgrade you haven't seen the issue yet.
After upgrade: it became orphaned by deleting sys_metadata. Now the property is inaccessible and it might cause issues.
Reproduced this OOB and filed a PRB for it. PRB1383590
Solution: Restore the instance from back-up. Fix the sys_class_names of the properties with empty sys_class_names and Upgrade the instance to Orlando.
This change will remove the records from sys_properties table, so that it can be imported again successfully.