I recently upgraded to the current version (184.108.40.206) of Sign-up Sheets Pro. I deleted all trashed posts as suggested under the other thread on this general topic. However, the database upgrade appears to stall at 3% and then starts over, and this keeps repeating.
One thing you can try is to increase the memory limit on your site temporarily while the migration runs. You can do so by adding the code below to your wp-config.php file…
define( 'WP_MEMORY_LIMIT', '256M' );
The above code is an example and you can adjust the amount 256M depending on your site and amount of data. If you rerun the migration and notice it gets to a higher percent but still gets stuck, try increasing the limit again. Once the migration is complete you can remove this from your wp-config.php as the migration will only need to be run once.
You can view your current memory limit within the WordPress admin under Tools > Site Health > Info (tab) > Server (accordion heading)
Please let me know if this resolves the issue otherwise I can debug further.