The same thing just happened to me. I have been using 2019.24.4. The car notified me an update was available and offered to install it overnight, at 2:00 am on Thursday. I accepted. When I got into the car the next morning, no update had been installed. In the evening, the car display's "software update" panel displayed "downloading software" with a solid green bar (like a completed progress bar). Two hours later that had not changed. I didn't seen any option in the car for actually starting the update. The phone still showed the update as being scheduled for 2:00 on Thursday, but also offered to start the update right away, which I did. A two minute timer started. When I touched the timer, it reset to 0:01 then immediately started.
Oddly, 13 minutes later, my phone notified me the the upgrade was beginning. Maybe it had spent all that time downloading files? Anyway, it's now finished, and I have 2019.28.3.1. I'd like to know why the scheduled update didn't happen, though. The car was sitting in the garage, with the same connectivity, both evenings. Actually I would appreciate more transparency in the update process. I wish it would tell me what version was available, notify me when it had downloaded the update and authenticated it, and then let me authorize or schedule the actual installation, and finally notify me when the update is complete. It would be nice if I could browse through the release notes before authorizing the installation.