i posted this question under this discussion and then realised it was marked as solved so may not be seen.
i use a combination of ACF’s gallery field and the simple lightbox wordpress plugin in most sites, and never see a problem, but in this case i cannot get it to work. images simply open as you would expect with no lightbox. the appropriate html is being added to the page but the functionality just fails to fire. no errors rthat i can see in the console.