On the Android app, the thumbnail will be updated a few seconds after the annotations are inputted last time. For this reason, you need to stay 3~5 seconds on the document This is to prevent performance degradations and we will improve how it works through future updates.
In case thumbnails are not updated
You need to stay on the document for 3~5 seconds after the annotations are inputted last time to update thumbnails.
If you move to the page manager or the file manager before thumbnails are updated, open the document again and wait approximately 3 seconds and then go back to the page manager or the file manager.
In case thumbnails are blank
Clear the cache doesn't affect your data on the app but by clearing the cache, the thumbnails can also be cleared.
But don't worry. If you update the data of the page of the document, the annotations will be recovered.