Hypervisor Hyper-V:  When testing the Host connections in Studio, one Delivery controller displays this error in the report: 

"Controller "DDC's FQDN": Object reference not set to an instance of an object. An unexpected error occurred. Check the hypervisor connection."

Uninstall Microsoft SCVMM console and reinstall to fix the issue

The console installation gives the machine the ability to make SCVMM calls to the Hyper-V hypervisor.  It takes about 5 minutes to uninstall and re-install.

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Problem Cause

When the Host Connection test is executed, it uses the locally installed SCVMM console to verify the capabilities of each Delivery Controller. 
In this customer's case, the SCVMM console would open fine on the delivery controller named as failed in the test and there was no other error. 

Hypervisor Hyper-V: When testing the Host connections in Studio, one Delivery controller displays this error in the report: "Controller labdc3.domain.local: Object reference not set to an instance of an object. An unexpected error occurred. Check the hypervisor connection."

Install the SCVMM Console:  Microsoft- Install the VMM Console