getting forbidden message

Hi,
I'm considering fully standardizing on Defender for all my site security. I'm using wordfence on some sites now and get the error below sometimes when I try to save. Any idea what causes this?

403 Forbidden

A potentially unsafe operation has been detected in your request to this site, and has been blocked by Wordfence.

If you are an administrator and you are certain this is a false positive, you can automatically whitelist this request and repeat the same action.

I am certain this is a false positive.

Whitelist This Action