Hi,
Please note that it sounds like the Wordfence scan stopped on an item. It's not stuck and constantly consuming reseources even though it looks that way. The scan simply stopped. Just in case you were worried about your site being slowed down.
Can you please go to the bottom of the Wordfence 'options' page. Click the link to test your Wordfence hosts available memory. Then post the results here.
Regards,
Mark.