CF7 broken in admin area, but still working on live site

I need to edit a contact form, every attempt to do this sends me to the homepage of my site as soon as I press save to update the form details, on return to the CF7 settings no changes have been saved.

It’s my own theme, using as few plugins as possible.

It works fine on a dev site.

I have uninstalled cf7, deleted and reinstalled – no luck.

I have disabled all other plugins that may have been causing conflicts – no luck.

I attempted to import contact forms from the dev site – behaves the same as usual, sending me to home page of my site.

I have searched everywhere looking for someone with a similar issue – again, no luck.

My next step is to remove cf7 completely and rebuild around a different plugin, but am loathe to do this due to the extra work this involves.

Please help!!