Placeholder text not updating

Really great plugin which I have been using happily for years, however I now have a really strange problem. I cannot update the placeholder text. I had already added some custom text to replace the standard ‘search’ but now I cannot get any new custom placeholder text to display on the front end – it just displays the old text. I have altered the text in Search Form > Text for search field. 

To test this I have:

– Cleared all caches on the server (including CDN)

– Cleared browser caches

– Deleted and re-installed the plugin

I am at a loss as to why it won’t update and can’t think of other things to try. Any ideas or suggestions? Thanks