I created a timeline a few weeks ago and returned to it to find nearly all of the articles gone. At the time, I did not think to check if all of the Historical Events had been deleted as well, so I recreated each of them in the timeline. They were fine for several hours, and now the timeline is blank again. This time I checked the Historical Events and they all still exist (I have two or three duplicates of several of them at this point) but they had been removed from the timeline.

1. Create timeline.
2. Create historical event articles in timeline.