I realise this is an old post but I had the same problem today. I engaged Microsoft Enterprise support and they were very quick with the solution. I thought I'd add it here in case anyone else gets the same issue and stumbles across this post. The issue I experienced was the cluster I was upgrading, despite the fact it was originally built using Windows Server 2016, had a cluster functional level of 8, which is Windows Server 2012 R2. As you can only perform a rolling OS upgrade by one iteration of Windows Server, the cluster was rejecting the Server 2019 node I was trying to add. Table of functional levels below:
Value Functional level
8 Windows Server 2012 R2
9 Windows Server 2016
10 Windows Server 2019
Run the following PowerShell command on a cluster node to verify the functional level:
Get-Cluster | Select ClusterFunctionalLevel
If you get a value of 8, then use the cmdlet: Update-ClusterFunctionalLevel to raise the functional level to Windows Server 2016 and try re-adding the 2019 node again.
Hope this post helps anyone who has this issue in future.