Hi Natasha,

using iD is not a good choice when dealing with relations. Here, some ways have been split, causing some troubles with bus relations

Kindly see the effect @ 

https://ptna.openstreetmap.de/results/DE/NI/DE-NI-VOS-Analysis.html#bus_N1

https://ptna.openstreetmap.de/results/DE/NI/DE-NI-VOS-Analysis.html#bus_N18

https://ptna.openstreetmap.de/results/DE/NI/DE-NI-VOS-Analysis.html#bus_515

https://ptna.openstreetmap.de/results/DE/NI/DE-NI-VOS-Analysis.html#bus_533

and so on, where PTNA complains about 2 things:

- relation now has gaps (Lücken), has x segments

- route follows a oneway ways  (Einbahnstraßen) in wrong direction (Richtung)

I suggest using JOSM for further (professional) edits.
It complains about gaps before the upload of changed data.
PTNA is currently the only QA tool checking for oneway ways being used in wrong direction.

Of course, JOSM has some learning curve but it is worth trying for day by day edits.

Regards
Toni (he)