I had this exact same problem on Wednesday night. In fact, I thought there was an issue with the AI server and kept putting off riding until I at least saw the AIs…but I did see other riders in the initial pop up list…but like you when I logged in I was the only name in the on screen rider list.
I even logged in once and tried to join another rider that showed in the initial popup, but when I was placed on the course there were no other riders and no AIs.
I sent a note to support who confirmed that the AI server was up and working and there were other people riding.
I was online and riding last night and I saw you log in. Your name was in my rider list and it showed how far ahead/behind me you were on the course. It just seemed we were on opposite sides of the course and our paths never crossed. You were displayed in my rider list the entire time you were online. I saw when you dropped off. I even noticed you logged back in again briefly as it looked like you tried to join me because your name appeared right behind me on the hill. In fact, I slowed down a bit to give you time to get going once I saw your name there, but then you dropped out again.
I did see other riders. A few were idle but I saw others riding…and I saw lots of AIs.