I scrolled back to my first activity on my.zwift.com (12/15/2015), but when I selected it, I was taken to a page with a throbbing multicolored Zwift logo. Ten minutes have gone by, and still no activity details. Just a big Z.
The same thing happens for my ride on 7/13/2018, and many others. In fact, this seems to be the case for all activities prior to 8/2/2018.