Beginner Gardening: Normal dieback or something more?, 2 by RoryPup

RoryPup wrote:
Here's some pictures of the white lilac. First picture is two of the larger plants. The one on the left didn't have much dead. The one on the right had about half dead that I cut out. Second picture is a close up of a part that due that I haven't cut out yet. Third picture is something I just noticed in the end of some new growth. It's actually in several places. Last picture shows the flowers. There weren't many flowers this year but that could be due to my trimming last year (before I knew they were lilacs and how to trim lilacs).