This is a bit of an odd one… see the screenshot.
Initially, ValveName was an internal property that was bound to an expression. Then I deleted it, but decided I needed it after all straight afterwards and undid the deletion, however how it’s a template parameter, and is still bound to the expression, with no way to unbind it
Edit: It actually shows that it’s template parameter in the properties editor. Creating it again in the Internal Properties and removing it from the Template Parameters and pressing OK then fixes it.