Clarity 16.3.X, 16.4.X
This is caused by DE181001
Within the current design, when you deactivate an attribute in Studio > Objects, it actually attempts to deactivate the rules where the attribute is present.
In Blueprint --> Actions, if you disable a process action, it is not until you drill down into the rule, that the UI detects that it is no longer valid. The UI will then correct the invalid data and will set the rule to disabled when saving. The user will see a banner indicating this.
New feature work will be needed to implement a different approach. The defect has been converted to a user story to work on a new feature that addressees this.