Most DrezSync issues come down to one of three things: the Google connection, caching, or a timezone or calendar mismatch. Run these four checks first. They resolve the large majority of problems before you need a specific article.
1. Check the plugin version
Go to Forms > Settings > DrezSync and look at the bottom of the screen. It shows the installed version. If that number is not the version you just uploaded, the install did not take, usually because of caching or an incomplete upload. Reinstall and confirm the number changes before troubleshooting anything else.
2. Confirm Google is connected
The same settings screen should say Connected. If it says Not connected, fix the connection first. See the article on connection setup problems.
3. Confirm the field has a Google Calendar ID
Edit your form, click the DrezSync Booking field, and make sure the Google Calendar ID box is filled in with the calendar you expect bookings to use. An empty or wrong calendar ID is a common cause of missing times and confusing availability.
4. Confirm your timezones match
Your WordPress timezone and your Google Calendar timezone must be the same, and both should be set to a city, not a fixed UTC offset. A city keeps daylight saving correct. In WordPress this is Settings > General > Timezone. A mismatch here causes the most confusing symptoms, such as the wrong times being blocked.
One more habit
If you changed a setting and the form did not change, it is almost always caching. Clear your cache and test again using the Gravity Forms preview. See the caching article.