The reason this has just started happening (albeit prematurely) can be found here: Simple Delivery | UK Seller Centre.
One of the FAQs states:
"Can I still use business policies?
Starting 7 April, certain features on the eBay app will no longer be supported. This includes business policies, the ability to set a handling time of more than 3 days, adding a custom SKU, subtitle, and Global Trade Item Number, and using the Gallery Plus feature.
You’ll still be able to use business policies when listing through your web browser, but if you’d prefer to list using the app, you can disable business policies in My eBay. The policies set on your existing listings will not be affected."
So, going forward, private sellers won't be able to list using Business Policies on the app (except, maybe, for items which are exempt from Simple Delivery? - I'm unsure on that).
