There is no longer an SCM change when using Multibranch Pipeline.
"Started by an SCM change"
Instead when the git server executes notifyCommit the branch that has changes shows "Branch indexing" and a question mark. Though at least the changes from SCM are shown on each build.
Its just that Branch indexing with a Question mark does not look good. Though when the build completes the question mark is gone. Better yet the --/++ badge icon indicating an SCM change should be used. At least when I start a build manually it shows "Started by user *****" as tooltip on the user badge icon.