Error when editing rule

I'm getting an error 'required field missing or not passing validation. The highlighted fields are are not changing, so I am not sure what is causing this error.

Stupid question time but I'm assuming you are trying to put in a button number and it is not taking it.

I get error when I click on anything. On other rules when I want to change an existing rule I click on it and it let’s me make changes.

It sounds like it must have somehow become corrupted.
Might be easier to just re-write into a new rule and delete the old one.