Also, FYI, I'm using the Mac version of the program.
I probably don't have an answer for your situation, but could you close out the project for a bit. Then, reopen the project, and display it how you wish it to look when exported. Example, "After the Fall", just below the dates, and closing/minimizing the unwanted Arcs, as you described in your first post? Once that's all done, save the project. Then close the project. Then open the project once more, (That last project close, should have preserved your initial view of the Timeline project) and go to export as you are want to do. 321 CE to 1500 CE. If it works, great! If not try repeating the processes mentioned above, but pick between 321 CE and 2010 CE, the end of your project. If it glitches, constantly at that same image, swap it out with suitable substitute. Maybe it's the image itself causing the glitch and of timeline moving 200 years. Maybe also try export without that image. I assume you have access to the image outside of the project, somewhere on your HDD.
Thanks for the suggestions. I'll give them a shot and hopefully IT support will show up with something more concrete if that doesn't work.