I came across this problem as well. Looking at the code I think the issue is that the offset
column on the wp_wpb2d_processed_files
table should be auto-increment.
I was able to resolve the issue by making this change to that table:
ALTER TABLE wp_wpb2d_processed_files
ADD INDEX 'offset' ('offset'),
CHANGE 'offset' 'offset' INT(11) NOT NULL AUTO_INCREMENT;
I don’t think that this change will be preserved when the plugin is updated, so if there is a future update that doesn’t fix this bug, you’ll need to re-run this statement after the update.