Win10Ent Build 1703 user here reporting what I've noticed after today's testing compatibility in regards to Windows Defender & Immunet.
After updating to Build 1703 I noticed that Windows Defender stops doing real-time protection and Windows starts reporting Immunet in system notifications as the system antivirus. However this seems to be by design for Windows Defender and Windows as noted here in the a recent MS page for Windows Defender Security Center app
If you switch Real-time protection off, it will automatically turn back on after a short delay. This is to ensure you are protected from malware and threats. If you install another antivirus product, Windows Defender AV will automatically disable itself and will indicate this in the Windows Defender Security Center app. A setting will appear that will allow you to enable limited periodic scanning.
I have version 184.108.40.20685 installed.