Hi again
Just had another thought…
I tried swapping to a different page on this site that was a top level menu item (not a CPT either) and it worked OK. (Using is-page)
Then I tried a second-level menu-item and that worked too.
I did that because the page that is a CPT of Service is also a second/sub-level menu item – just to try and eliminate that. However seems it may be the CPT thats the root cause?
cheers