Error 543 There was an error during heartbeat communicating to primary federation server

Question

After I joined Windows Server 2019 servers to an existing ADFS Farm running on Windows Server 2016, the ADFS-event log on the ADFS 2019 (secondary servers) keeps reporting this error:

There was an error during heartbeat communicating to primary federation server.
Primary server: 'ADFSserver'
Endpoint: 'http://ADFSserver/adfs/services/policystoretransfer'
Additional data
Exception details:
System.ServiceModel.FaultException: The formatter threw an exception while trying to deserialize the message: There was an error while trying to deserialize parameter http://schemas.microsoft.com/ws/2009/12/identityserver/protocols/policystore:maxBehaviorLevel. The InnerException message was 'Invalid enum value 'Win2019' cannot be deserialized into type 'Microsoft.IdentityServer.FarmBehavior'. Ensure that the necessary enum values are present and are marked with EnumMemberAttribute attribute if the type has DataContractAttribute attribute.'. Please see InnerException for more details.

Does anyone know why this error keeps on showing when the ADFS Farm consist of 2 Windows Server 2016 servers and 2 Windows Server 2019 servers?

The primaryComputer is still one of the Windows Server 2016-servers since the migration is not completed yet.
Original thread on technet asking the same thing:
https://social.technet.microsoft.com/Forums/scriptcenter/en-US/d1bb3be2-e7ff-4892-86dd-8ab402556153/adfs-error-543-there-was-an-error-during-heartbeat-communicating-to-primary-federation-server?forum=ADFS