I'm wondering if anyone else has been able to utilize the on-screen keyboard at the Drive Encryption pre-boot authentication screen using a Surface Book model 1703? When attempting to use the OSK at the pre-boot screen, it responds about one out of every ten attempts. We had a similar problem with the Surface Pro 4, but were able to resolve that by following McAfee KB81900. McAfee Support is advising us that that they are unable to assist further as the Surface Book fails the tablet test tool referenced in KB78050 (error: UEFI Pre-Boot Support: Unsupported – Touch scaling is incorrect). They're indicating that the Surface Book is missing a UEFI protocol or that there is a UEFI protocol defect, and that DE will not be updated to accommodate it. I've updated the Surface Book firmware to the latest release from June 21st, but still no luck getting the drivers to show as supported. It seems odd that a newer tablet model such as this would not be running the firmware that DE needs to utilize the OSK.
Moved provisionally to Encryption: EEM Managed for faster handling