WordPress keeps renaming my post url to a different name

WordPress keeps renaming my post URLs automatically.

I have this issue with at least 2 of my posts but I haven’t checked any other ones. I have the following 2 posts:

https://www.greenthickies.com/apricot-mango-spinach-smoothie-signed-organic-veg-box and

https://www.greenthickies.com/chocolate-cherry-smoothie/

A few times over the last few days when I’ve loaded the post up, it redirects to the home page as it can’t be found. When I go in to edit the post I see it has changed the URL of both posts to:

https://www.greenthickies.com/strawberry-spinach-salad-smoothie-2/

Which is the name of one of my other posts (without the 2 on the end). I keep changing the URL, updating the post. It works for a while and reverts back to the wrong URL again.

Please can anyone help me as this is causing all kinds of problems.

Many thanks

Katherine