Sorry to necro an old thread, but this bug appears to arise from copying an existing timeline. The new copy of the timeline will fire the finish trigger at the same end point of the old timeline regardless of it’s own timeline length.
Eg. You have an existing timeline that’s 1 second long. You copy it and set the length of the new timeline to 2 seconds. The new timeline will fire its finish trigger at 1 second regardless of the fact that its a 2 second timeline. This bug exists even if you reduce the length of the new timeline, resulting in the finish trigger firing late instead of early.