Cause

This issue can occur if the Volume Shadow Copy Service (VSS) writers did not respond to a query from the VSS service (OS level operation).

Traceback

1. Follow the instructions provided in the Logs article to retrieve job logs.
2. Extract the logs and go to Phoenix<YYYYMMDD>_<timestamp>.log file to see the below traceback in the logs:
   [2021-08-05 20:00:59,266] [ERROR] <_MainThread(MainThread)> HypervAgent: Hyperv backup failed: Vss Error: Operation timedout of gathering writer metadata hr = -2147212520
   [2021-08-05 20:00:59,267] [ERROR] <_MainThread(MainThread)> Error <class 'pyvss.VssException'>:Vss Error: Operation timedout of gathering writer metadata hr = -2147212520. Traceback -Traceback (most recent call last):
   File "agentPartnerProcess.pyc", line 85, in _process_request_start
   File "agents\hyperv\hypervAgent.pyc", line 68, in process_backup_start
   File "agents\hyperv\hypervBackup.pyc", line 341, in prepare
   File "agents\hyperv\vssHelper.pyc", line 127, in discover_vm
   File "agents\hyperv\hypervVssUtils.pyc", line 155, in gather_writer_metadata
   VssException: Vss Error: Operation timedout of gathering writer metadata hr = -2147212520

Event viewer:

Log Name: Application
Source: VSS
Event ID: 12347
Task Category: None
Level: Error
Keywords: Classic
User: N/A
Computer: abcd.Example.net
Description:
Volume Shadow Copy Service error: An internal inconsistency was detected in trying to contact shadow copy service writers. The Registry Writer failed to respond to a query from VSS. Check to see that the Event Service and Volume Shadow Copy Service are operating properly, and please check the Application event log for any other events.

Operation:
Gathering Writer Data
Executing Asynchronous Operation 
 

Scenario 1

1. Run the command vssadmin list writers and make sure all VSS writers are stable. 
2. Follow the instructions in the Microsoft article Event ID 12347 — Volume Shadow Copy Service Operations.
3. Rebooting the Hyper-V host may resolve the issue.

Scenario 2

1. The command vssadmin list writers doesn’t report any output.
2. Follow the instructions in the Microsoft article No VSS writers are listed when you run the vssadmin list writers command in Windows Server.
3. Rebooting the Hyper-V host may resolve the issue.