Hi @play33
Thanks for reaching us and sorry for the inconvenience.
We have tried to reproduce the issue on our test site by updating the plugin to it’s latest version but unfortunately we couldn’t recreate such and issue and we are being able to edit feeds without having any errors which indicates the issue you are experiencing could be a site specific issue.
In this situation, I would suggest you to delete the plugin and then reinstall and activate a new file by downloading it from the WordPress directory and try editing the existing feeds again. NB: Deleting the plugin won’t remove your old data.
However, if none of the above helps you to resolve the issue, please, roll back to the previous version 5.4.9 from here. Please, see this screenshot to know where to download the old version.
Once the old version is downloaded, deactivate and delete the current version and then install and activate the newly downloaded plugin file.
For more, please, contact us from here.
Best regards,