In Director some DDCs appear to be offline .
However the DDCs in question are working fine and are brokering ICA connections. Studio can be opened from the DDC console.

Engage Networking team and ensure that traffic on port 80 is not  blocked between the DDC and the Director Server.

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Problem Cause

The Director server and the DDCs that are marked offline are in different subnets.
A firewall between the Director and the DDC is dropping packets.

This can be observed in a CDF trace.

497,0,2023-02-08 12:29:17:58697,9804,8936,Unknown,-1,DirectorService,,0,,1,Error,"[t:398, s:unknown]CommunicationException caught: An error occurred while receiving the HTTP response to http://xxx.xxx.xxx/Citrix/ConfigurationContract/v2. This could be due to the service endpoint binding not using the HTTP protocol. This could also be due to an HTTP request context being aborted by the server (possibly due to the service shutting down). See server logs for more details.","TraceId=4bc75a33ee6c164b90bad38c0abe5757, SpanId=ce2b43d86b62be43, TransactionId=4bc75a33-ee6c-164b-90ba-d38c0abe5757"
498,0,2023-02-08 12:29:17:58707,9804,8936,Unknown,-1,DirectorService,,0,,1,Information,"[t:398, s:unknown]Connector has faulted. Disposing.","TraceId=4bc75a33ee6c164b90bad38c0abe5757, SpanId=ce2b43d86b62be43, TransactionId=4bc75a33-ee6c-164b-90ba-d38c0abe5757"

A Network trace shows that packets sent from the Director Server and never received by the DDC.

From Director Server 



Highlighted packet is never received by the DDC

On DDC 




A RST packet is subsequently sent by both sides  to  break the network connection.

The  firewall logs show that packets on port 80 are dropped.