I came across this situation after updated one of my notebooks and sync. Then I found name of the notebook was highlighted with no explanation or note for that highlight. Have anybody had this situation before and how to resolve the situation? It is getting a bit annoying.

I found my problem. I looked into the sections of that problem notebook and found one of the section was highlighted with boldtype as well. Fortunately, there was one page with an embedded (inserted file) and I deleted that. The highlight went away.

The problem with Onenote is when there are conflicts inside the notebooks, the sections or the pages, there is seldom any notice or the nature of the conflect. Users have to trial by error to fix it.