wordpress category page 404 -

I have updated a category slug and are now displaying my category page 404 for that category. I have a staging site and it works fine but when I do this for some reason, I get 404. I have,

• Repeated permalinks
• Disabled plugins
• Disable all caching
• Restart my server

I'm completely confused and do not understand why WordPress is so weak that permalinks and url.

Thanks