The pool managing the instance is not available or the location monitoring object cannot be found - discovery progress

Navigate to C:\Program Files\Microsoft System Center 2016\Operations Manager\Server

Open (as administrator) ConfigService.config

Edit the following lines, removing the \INSTANCENAME values so that only the SQL server value is shown.

     <Category Name="Cmdb">

        <Setting Name="ServerName" Value="jimmy\jimmy" />

        <Setting Name="DatabaseName" Value="OperationsManager" />

      <Category Name="ConfigStore">

        <Setting Name="ServerName" Value="jimmy\jimmy"  />

        <Setting Name="DatabaseName" Value="OperationsManager" />

To

     <Category Name="Cmdb">

        <Setting Name="ServerName" Value="jimmy" />

        <Setting Name="DatabaseName" Value="OperationsManager" />

      <Category Name="ConfigStore">

        <Setting Name="ServerName" Value="jimmy" />

        <Setting Name="DatabaseName" Value="OperationsManager" />

                   

Restart System Center Management Configuration and System Center Data Access Service.

Issue with SCOM agent in forest trust domain(0x80090311)

If you see these events 20057 with code (0x80090311), that is mean (trust is corrupted) and agents can not authenticate to MS.

The most common reason is Firewall issue.
(TCP/UDP 88 port (Kerberos) and TCP/UDP 389 port (LDAP)) should be open from Agent to Management Server DCs.