That makes me think something in the tables might be corrupt from the downgrade to free.
A complete re-install of Wordfence might be a good step. It’s always best to make a backup of the site and database before installing/removing plugins, just to be safe.
Additionally, you can backup your Wordfence settings via the Export option. Navigate to Wordfence > Tools > Import/Export Options and click Export. You can also take note of the current Whitelisted URLs you have in Wordfence > Firewall > All Firewall Options > Whitelisted URLs as these are NOT included in the Import/Export, and will be lost during the re-install.
Here is what is exported: https://www.wordfence.com/help/tools/import-export/
During the export, you will be given a long string of text. Keep this safe, you’ll need it in a few minutes.
After that, enable the option to Delete Wordfence tables and data on deactivation in All Options > General Wordfence Options. You will want to remember to disable this after you reinstall Wordfence again.
After you enable that option, you can deactivate Wordfence from the Plugins area of your site, then delete it. Next, from the plugins area, search for and re-install Wordfence like normal.
It will be like setting Wordfence up for the first time. You will need to enter an email address, and then go into Tools > Import/Export Options and paste that string of text into the Import Wordfence Options field and click the button there.
The firewall will be in Learning Mode by default for 7 days. I would recommend switching this to Enabled and Protected as soon as possible.
Let me know if this resolves it!
Thanks!