What does this mean - what is being registered?

it is on a 2016 server version:

Log Name: Microsoft-Windows-User Device Registration/Admin
Source: Microsoft-Windows-User Device Registration
Date: 19/09/2020 11:55:02
Event ID: 304
Task Category: None
Level: Error
Keywords:
User: SYSTEM
Computer: DC1.domain.local
Description:
Automatic registration failed at join phase. Exit code: Unknown HResult Error code: 0x801c001d. Server error: empty. Debug Output:\r\n joinMode: Join
drsInstance: undefined
registrationType: undefined
tenantType: undefined
tenantId: undefined
configLocation: undefined
errorPhase: discover
adalCorrelationId: undefined
adalLog: undefined
adalLog: undefined
adalResponseCode: 0x0
.
Event Xml:



304
0
2
0
0
0x8000000000000000

56


Microsoft-Windows-User Device Registration/Admin
DC1.domain.local



-2145648611
empty
joinMode: Join
drsInstance: undefined
registrationType: undefined
tenantType: undefined
tenantId: undefined
configLocation: undefined
errorPhase: discover
adalCorrelationId: undefined
adalLog: undefined
adalLog: undefined
adalResponseCode: 0x0

Is this an upgraded SBS Small Business Server domain?

If not have you added any GPO stuff regarding automatic domain join or Azure join?

Have a check through with GPResult on your domain group policy and let us know back here.

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