During a 26 mile ride the program stopped working twice and I had to re-start it losing the data. Also while ascending Col de Zwift I turned around went down to the bottom and then I turned again and I had to climb again.
You might want to submit a request to their support team (top of the page) and attach your C:\Documents\Zwift\Logs\Log.txt and the Launcher_log.txt for app crashes. I had a recent issue with it myself a few weeks ago after an update and re-installing zwift fixed it, but you probably want to do it the proper way so they can get your logs lol.
Also, if you check DOCUMENTS/ZWIFT/ACTIVITIES you may find your ride data is there.
Ever since the last update, I have been crashing every ride, anywhere from 35 minutes to 80 minutes in. Maybe I’ll try the uninstall/reinstall thing. I have submitted my logs.