Some tiles show things not visible in the data layer. For example, https://tile.openstreetmap.org/17/64986/41952.png which should be empty but contains a boundary. How can the data used in a tile be found?
Where is that?
You have to have the edges of the boundary in your data layer. The way itself won’t be shown without any nodes. Because the way is created based on the nodes and is not a physical object.
It is the nearly horizontal boundary on this part of the map: https://www.openstreetmap.org/#map=15/54.2137/-1.5146.
This boundary segment is not shown in JOSM.
There a more “phantom boundaries” like that:
May be the render database needs a full reload?
That might not work in this case. The same artefact appears at https://map.atownsend.org.uk/maps/map/map.html#zoom=15&lat=54.2124&lon=-1.51015 if you turn the boundaries overlay on - see e.g. https://map.atownsend.org.uk/hot2/15/16247/10488.png .
That boundaries layer was done as a one-off import of “europe_2018-11-23T21:14:02Z.osm.pbf” on 25th November, just before I wrote https://www.openstreetmap.org/user/SomeoneElse/diary . Using overpass I can’t find any historic way on that alignment.
Seems to be a renderer issue. ÖPNV map does not show a border here: https://www.öpnvkarte.de/#-1.5026;54.215;14