Issues connecting to EMS PowerShell after update

Hi,

We recently upgraded one of our Exchange 2019 Hybrid servers to CU12 (from a much older CU). Which has now completed successfully after a couple of tries. 

During our testing though we found that the EMS doesn't connect. The EMS window doesn't give any useful error, the error message reason is blank. Everything else on the server appears functional and suggests the update was successful except for the EMS. 

In the HTTPProxy log though I can see this error which says the connection was forcibly closed by the server. It does mention TLS also. 

I've compared the TLS settings in this registry location to a server which hasn't been upgraded yet and they look the same to me:

Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols

Has anyone seen this before? Was the connection method/security changes in the last half dozen CUs? 

WebExceptionStatus=SendFailure;WebException=System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a send. ---> System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host at System.Net.Sockets.Socket.EndReceive(IAsyncResult asyncResult) at System.Net.Sockets.NetworkStream.EndRead(IAsyncResult asyncResult) --- End of inner exception stack trace --- at System.Net.TlsStream.EndWrite(IAsyncResult asyncResult) at System.Net.ConnectStream.WriteHeadersCallback(IAsyncResult ar) --- End of inner exception stack trace --- at System.Net.HttpWebRequest.EndGetRequestStream(IAsyncResult asyncResult TransportContext& context) at System.Net.HttpWebRequest.EndGetRequestStream(IAsyncResult asyncResult) at Microsoft.Exchange.HttpProxy.ProxyRequestHandler.<>c__DisplayClass199_0.<OnRequestStreamReady>b__0();SharedCache=AMCacheRemovalFailure;WillRetryOnError(1/2)-LastTryData=TotalRequestTime:10 Delay:0 State:ProxyRequestData AnchorMailbox:ServerVersion~Version 15.2 (Build 1117.7)