This boundary is both for the city and for the admin boundary level 6 which is also for the city, this is in effect a duplication with the result that there are two osm_ids for the same thing. The information regarding the wikidata, population and alternative translations of names is missing from the admin level as they have been entered for the city.

Unclosed polygon #1405412

Details shown by -
WAY_id: 279377676
REL_id: 3715237

Others parts missing on same poly and may other on the admin polygons for Belgium. If I can of assistance please let me know what to send.
For the future is there a good tutorial page for editing myself?
Regards