Update (Sep 27, 2017): This issue has been fixed by Apple. The Apple server communication and iOS erasure should work again with all previous versions of Blancco Mobile Device EraserDiagnostics and Erasure.
On September 25th 2017, Apple changed the user-agent that is used with communicating with the Apple iOS software signing server, which stopped all (except MacOS) versions of iTunes from working (Apple has since released the fixed iTunes versions). Since Blancco's iOS erasure also works thru Apple servers, this caused an issue where iOS device erasure was failing around 22%.
Blancco has released Blancco Mobile Device Eraser Diagnostics and Erasure (BMDE) version 3.3 that among other things, addresses this issue with the iPhone erasure. The update is available via Blancco's OTA (Over-The-Air) download server, by downloading and updating the version straight from the Blancco Mobile Device Eraser Diagnostics and Erasure software over internet connection. Release notes can be found here.