Hundreds of duplicate posts!!!

Hi all, we are having a perplexing issue. Sometime today all new posts coming in to our WP site have been getting duplicated hundreds of times. We use the uCan Post plugin, and it has been functioning just fine for about a year. The weird thing is that the duplicated posts do not appear in the uCan Post queue, they go straight to the pending list.

What would cause a post to be re-submitted in a loop? I have not found anything odd in the uCan Post code, we tried uninstalling and reinstalling it. I have spent a bit of time checking for malicious activity on the site, and couldn’t find anything out of the ordinary.

I need a clue about where to begin looking in the code. Thanks for any help.