What happens if you press the stop button on the companion app?And does it show as an activity in your Zwift profile?
Can you log into Zwift via a web browser, and find your ride data there? You may be able to download the data and manually upload it to Strava or wherever you upload your ride data.
Try the '3x tap on the Zwift logo' trick from here: https://zwiftinsider.com/retrieve-lost-ride/