Errors in Sitemap tool, can it be reset?

[Dandroid5000]

The Sitemap plugin has stopped displaying in our integration site and the sitemap.xml path is returning a 404. Also, the icon is no longer visible in the cms. There is no role restriction for it.

It's enabled under plugins:

It's still working fine in our local and staging environments. It seems to be related to the database somehow.

Note, I can run the scheduled job to build the sitemap without errors.

Here's what we're seeing under the logs if we navigate to sitemap.xml

Two questions:

1. How can I find the source of the 'System.ArgumentNullException: Value cannot be null. (Parameter 'uriString')'?
2. Is there a way to reset the sitemap tool? i.e. wipe it from the database and start again?

Any other ideas?

Thanks in advance
Dan