It seems that this error appears when backup was created on the old version on WooCommerce and you restore it on the new version:
How to fix Failed to create tmp table _fwbk_wp_wc_download_log. Duplicate foreign key constraint name 'fk_wp_wc_download_log_permission_id'
I have fixed this by adding an additional check here
wp-content/plugins/unyson/framework/extensions/backups/includes/module/tasks/type/class-fw-ext-backups-task-type-db-restore.php
Try to replace this code:
foreach ( $line['data']['indexes'] as $index ) {
$cols_sql[] = $index;
}
To this one:
foreach ( $line['data']['indexes'] as $index ) {
if ( ! strpos($index,'fk_wp_wc_download_log_permission_id')){
$cols_sql[] = $index;
}
}
This worked for me