We also have these errors:
Log Name: Directory Service
Date: 04/03/2020 19:08:34
Event ID: 1925
Task Category: Knowledge Consistency Checker
User: ANONYMOUS LOGON
The attempt to establish a replication link for the following writable directory partition failed.
Source directory service:
Source directory service address:
Intersite transport (if any):
This directory service will be unable to replicate with the source directory service until this problem is corrected.
Verify if the source directory service is accessible or network connectivity is available.
1722 The RPC server is unavailable.
192503100x808000000000000033619Directory ServicecompanyDC01.company.localDC=ForestDnsZones,DC=company,DC=local2f8a5d79-4bd8-4872-bef5-2ad09c467893._msdcs.company.localThe RPC server is unavailable.CN=NTDS Settings,CN=companyLON-DC01,CN=Servers,CN=London,CN=Sites,CN=Configuration,DC=company,DC=localCN=IP,CN=Inter-Site Transports,CN=Sites,CN=Configuration,DC=company,DC=local1722
DC=ForestDnsZones,DC=company,DC=local2f8a5d79-4bd8-4872-bef5-2ad09c467893._msdcs.company.localThe RPC server is unavailable.CN=NTDS Settings,CN=companyLON-DC01,CN=Servers,CN=London,CN=Sites,CN=Configuration,DC=company,DC=localCN=IP,CN=Inter-Site Transports,CN=Sites,CN=Configuration,DC=company,DC=local1722
The RPC server is unavailable.
Log Name: File Replication Service
Date: 04/03/2020 19:02:56
Event ID: 13508
Task Category: None
The File Replication Service is having trouble enabling replication from companyLON-DC01 to companyDC01 for c:\windows\sysvol\domain using the DNS name companyLON-DC01.company.local. FRS will keep retrying.
Following are some of the reasons you would see this warning.
 FRS can not correctly resolve the DNS name companyLON-DC01.company.local from this computer.
 FRS is not running on companyLON-DC01.company.local.
 The topology information in the Active Directory Domain Services for this replica has not yet replicated to all the Domain Controllers.
This event log message will appear once per connection, After the problem is fixed you will see another event log message indicating that the connection has been established.
13508300x80000000000000522File Replication ServicecompanyDC01.company.localcompanyLON-DC01companyDC01c:\windows\sysvol\domaincompanyLON-DC01.company.localBA060000
13508300x80000000000000522File Replication ServicecompanyDC01.company.local
File Replication Service
Date: 04/03/2020 19:01:30
Event ID: 1126
Task Category: Global Catalog
Active Directory Domain Services was unable to establish a connection with the global catalog.
1355 The specified domain either does not exist or could not be contacted.
Make sure a global catalog is available in the forest, and is reachable from this domain controller. You may use the nltest utility to diagnose this problem.
1126021800x808000000000000033617Directory ServicecompanyDC01.company.local3200e241355The specified domain either does not exist or could not be contacted.
3200e241355The specified domain either does not exist or could not be contacted.
The specified domain either does not exist or could not be contacted.
Log Name: DNS Server
Date: 04/03/2020 18:46:41
Event ID: 4013
The DNS server is waiting for Active Directory Domain Services (AD DS) to signal that the initial synchronization of the directory has been completed. The DNS server service cannot start until the initial synchronization is complete because critical DNS data might not yet be replicated onto this domain controller. If events in the AD DS event log indicate that there is a problem with DNS name resolution, consider adding the IP address of another DNS server for this domain to the DNS server list in the Internet Protocol properties of this computer. This event will be logged every two minutes until AD DS has signaled that the initial synchronization has successfully completed.
Date: 04/03/2020 18:46:28
Event ID: 2886
Task Category: LDAP Interface
The security of this directory server can be significantly enhanced by configuring the server to reject SASL (Negotiate, Kerberos, NTLM, or Digest) LDAP binds that do not request signing (integrity verification) and LDAP simple binds that are performed on a cleartext (non-SSL/TLS-encrypted) connection. Even if no clients are using such binds, configuring the server to reject them will improve the security of this server.
Some clients may currently be relying on unsigned SASL binds or LDAP simple binds over a non-SSL/TLS connection, and will stop working if this configuration change is made. To assist in identifying these clients, if such binds occur this directory server will log a summary event once every 24 hours indicating how many such binds occurred. You are encouraged to configure those clients to not use such binds. Once no such events are observed for an extended period, it is recommended that you configure the server to reject such binds.
You can enable additional logging to log an event each time a client makes such a bind, including information on which client made the bind. To do so, please raise the setting for the "LDAP Interface Events" event logging category to level 2 or higher.
Date: 04/03/2020 18:36:00
Internal ID: 3200e24
1126021800x808000000000000033599Directory ServicecompanyDC01.company.local3200e241355The specified domain either does not exist or could not be contacted.
Presumably they are all related.. 😣