Hi Florian yeates, welcome to open street map! I see in this change set you've mapped out some houses and buildings in Plaistow, when adding things to the map they need to have the correct tags on them so the map knows how to show them. It looks like you've mapped the buildings but they have no tags on them so they don't show on the map. If you select the buildings in the editor and then select that they are buildings, or houses then that would be great.
Happy mapping, Jarv