OpenStreetMap

I can´t reproduce your error at this position, but it sounds like a error that can happen if you haven´t downloaded the whole multipolygon relation in iD-Editor. Then it´s only on your client, and you can fix it if you select the residential landuse relation and click the download icon for all parts.

Most times this error happens if there is a big Landuse Multipolygon with mutiples of members, but it can also happen in these smaller ones like here.

I can´t find a mapping error here, but maybe you could link to the park where the error occured, because there isn´t any park near the note´s position. The only inner member i can find here is a "landuse=allotments" (in germany we call them "Kleingarten", so thats what you could find on a sign, maybe they got something with "park" in their name, they can choose them freely).

I'm sorry, I should have been more clear.
You're right, the "park" I meant is actually of type "allotment".

I'm not using any offline client, just the openstreetmap.org website.

When clicking on coordinate 51.24160, 12.71546 to query features (https://www.openstreetmap.org/query?lat=51.24160&lon=12.71546) I would expect a "residential area" under "Enclosing features" or "Nearby features", specifically this feature: https://www.openstreetmap.org/relation/12802365

But it doesn't show up.

When using this coordinate: https://www.openstreetmap.org/query?lat=51.24194&lon=12.71562

the relation shows up under "Nearby features".

Why is that relation only detected when querying near the "allotment", but not anywhere else in the large "residential area"?

When you click on or near the allotment, it retrieves the allotment and hence the multipolygon.

When you click outside the allotment, it does not detect any member of the multipolygon and therefore does not show it. Multipolygons are treated differently than plain areas. I can only assume that nominatim's query feature simply does not check for multipolygons which contain the queried coordinate.

(On higher zoom levels, it will start working again, since the outer way(s) of the multipolygon are covered by the search query.)