If yesterday's Zwift ride is missing from Strava, start in Zwift. Can you open the completed activity there? Establish where the record stops before reconnecting accounts or trying to rebuild the ride from memory.
This guide is for a ride that was saved successfully in Zwift. A session missing from Zwift itself is a different problem and may need its own support investigation.
Check your own Strava activity list as well. Look at the date and start time, rather than relying on a feed notification. You want to establish that the ride is absent before attempting another upload.
There is a common expectation to clear up first. Strava's Zwift integration guide says historical activities do not sync automatically. Connecting the accounts now will not, by itself, bring across an earlier ride. The documented alternative is to download that activity's FIT file and upload it yourself.
On a computer, open your activity feed on the Zwift website and select Just Me. Find the ride, open its activity page, then use the gear icon to download the FIT file. Keep that downloaded copy while you complete the transfer.
Next, use the file upload page on the Strava website. Select the downloaded FIT file using Choose Files. Strava's activity upload guidance confirms that FIT files containing workout data are supported, with a maximum file size of 25MB.
Once the activity appears, open it. Compare its date, duration and available measurements with the saved Zwift ride. Check that you chose the right session before using it to review your training week. If an upload is rejected, note the exact message and follow the relevant support guidance rather than repeatedly changing the file.
Treat recovering this ride and checking future syncing as separate jobs. After your next ordinary ride, inspect both activity lists. A successful manual upload shows that this file arrived; it does not test the automatic connection.
This is a useful standard for MOTRA too: make the path from a completed workout to its record easy to follow.
Keep the troubleshooting anchored to three things: the saved activity, the file you transferred and the record that arrived. That gives you something concrete to verify at each stage.