Epic #72584: sysext:impexp
Relationship between tt_address and sys_category records broken on import
If you try to import tt_address records with assigned sys_category records the relationship records in sys_category_record_mm are broken afterwards.
There is one correct record with the value from field categories of the tt_address record as uid_local. This means that a category whose uid is the same as the number of assigned categories is now asigned to the tt_address record.
And then there are relationship records with the correct uid_local and uid_foreign values that are missing the value categories in field fieldname. This means that these relationships are not shown in the backend. This can easily be fixed by setting fieldname to categories.
I'm not sure if this is an issue with system extension impexp or extension tt_address or even just a configuration problem. Maybe someone else can confirm this bug.