Filter Manager failed to attach to volume '\Device\HarddiskVolume511'. This volume will be unavailable for filtering until a reboot. The final status was 0xC03A001C

We are seeing this error on Windows Foundation Server 2016 with a fairly new install:

Log Name:      System
Source:        Microsoft-Windows-FilterManager
Date:          16/09/2019 23:03:42
Event ID:      3
Task Category: None
Level:         Error
Keywords:      
User:          SYSTEM
Computer:      %computername%.DOMAIN.local
Description:
Filter Manager failed to attach to volume '\Device\HarddiskVolume511'.  This volume will be unavailable for filtering until a reboot.  The final status was 0xC03A001C.
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Microsoft-Windows-FilterManager" Guid="{F3C5E28E-63F6-49C7-A204-E48A1BC4B09D}" />
    <EventID>3</EventID>
    <Version>0</Version>
    <Level>2</Level>
    <Task>0</Task>
    <Opcode>0</Opcode>
    <Keywords>0x8000000000000000</Keywords>
    <TimeCreated SystemTime="2019-09-16T22:03:42.993351000Z" />
    <EventRecordID>75507</EventRecordID>
    <Correlation />
    <Execution ProcessID="4" ThreadID="6288" />
    <Channel>System</Channel>
    <Computer>%computername%.DOMAIN.local</Computer>
    <Security UserID="S-1-5-18" />
  </System>
  <EventData>
    <Data Name="FinalStatus">0xc03a001c</Data>
    <Data Name="ExtraStringLength">25</Data>
    <Data Name="ExtraString">\Device\HarddiskVolume511</Data>
  </EventData>
</Event>

any ideas?

This may well be that the disk attached for backup is being registered as a device at startup, but becomes unavailable to the system once Windows Backup gets a-hold of it for exclusive use, so the system considers it a failed device at time of backup.

You could pause Windows Search & Filter Set-up at start-up or perhaps set it to delayed start and see if it does not spot the backup devices before Windows Backup does.