Having investigated further, it seems that Virgin Broadband here in the UK is blocking BoostCommerce Product Filter and Search.
It has something to do with the Virgin Websafe settings:
Virus Safe and ChildSafe
If these are enabled then the APP does not work either in the Shopify backend or on the website
(on the back end the APP does not load and on the website the filters do not appear)
I have checked with another Virgin broadband user.. the APP is being blocked by Virgin 'Childsafe' setting.
FYI, we have launched Ultimate search and filter app that offers advanced tools for a smooth users' product discovery. The features includes Autocomplete for search and Dynamic product filtering (filter products by Product attributes such as Product type, collection, vendor, product tag, variants), Color Swatch Display, Merge values, Price slider, Product count for filter value, Breadcrumb trail (selected filter values). Moreover, you can utilize the power of AI technology in search (Synonym search, Natural language processing), Merchandising to promote your marketing campaigns (promote high-profit margin products, sales products, promotion banners) and Internal site search analytics.
BoostCommerce support have been excellent and they are trying to solve the issue with Virgin Media.
It looks like an over zealous Virgin bot has flagged the APP page up. it's obviously an error and hopefully will be fixed soon.
This only affects Virgin Broadband users with 'Child Safe' enabled on their connection.