Hi XioNoX,
assuming you would just use the OSM Inspector view mentioned above, lets zoom closer:

https://tools.geofabrik.de/osmi/?view=routing&lon=-4.46454&lat=48.43828&zoom=15&baselayer=Geofabrik%20Standard&overlays=duplicated_edges%2Cduplicated_edges%2Cduplicated_edges_areas

Now you can already see, there is something wrong with the three roundabouts.

Now click on one of the blue markers. A "selection" window will pop up, showing different icons to select your editor. Click on the icon with the stylized pencil. Now JOSM will open directly the affected ways.

To see an actual error message, you can select the complete roundabout area and then run the validator.

But you can also just click on a section of the roundabout with the middle mouse button to get a list, which ways are there laying on top of each other.

I f you are used to JOSM, you may know that connection points are makred slightly bigger than those nodes which are within a way. So this also gives a hint here as all connection points in the roundabout are big.
Guido
