Hi all,
I was working on a migration from Legacy to Unified Interface in a cloud environment.
I noticed that not all charts appear in every dashboard (this only happens in Unified Interface).
I fixed this bug by selecting the default view for each graph again. It may also appear that the chart is using an old view that has been deleted or is inactive. Try adding this view again and then publish your customizations.
You can also check if the view gives data and try to edit your chart directly in the specified entity.
Hope this helps!