"Unknown Devices"

Jessica_Korn
Level 3

"Unknown Devices"

I'm trying to identify where my emails are being opened. I've built smart reports with the filter "Opened Email" and I am using the constraints of "Is Mobile", "Device", "Platform", and "Browser" to choose from.

A large majority of my results (around 45%) are coming in as "unknown" device. Does anyone know the reason for this?