If you upgraded to version 2.3.7 of Organize Series and noticed a slowdown of your WordPress administration backend it is because of a leftover testing coding setup I left in the automatic upgrade script for Organize Series addons in the backend. I noticed the problem today while investigating the slowdown issues on my own sites and created a quick fix. Please upgrade to version 2.3.8 as soon as possible to replicate the fix to your own setup and you should notice some speed increase on your backend. Sorry I missed this folks!
You can read more about this via the changelog.