[op-creds] Fix RemoveFabric command

src/app/clusters/operational-credentials-server/operational-credentials-server.cpp

@@ -354,12 +354,14 @@ bool emberAfOperationalCredentialsClusterRemoveFabricCallback(app::CommandHandle
         FabricIndex currentFabricIndex        = commandObj->GetAccessingFabricIndex();
         if (currentFabricIndex == fabricBeingRemoved)
         {
-            // If the current fabric is being removed, expiring all the secure sessions causes crashes as
-            // the message sent by emberAfSendImmediateDefaultResponse() is still in the queue. Also, RMP
-            // retries to send the message and runs into issues.
-            // We are hijacking the exchange delegate here (as no more messages should be received on this exchange),
-            // and wait for it to close, before expiring the secure sessions for the fabric.
+            // If the current fabric is being removed, don't expire the secure sessions immediately as they are
+            // still needed to send a pending message generated by emberAfSendImmediateDefaultResponse().
+            // Hijack the exchange delegate here (as no more messages should be received on this exchange),
+            // and wait for it to close, before expiring the secure sessions for the fabric. Also, suppress MRP
+            // usage since the MRP engine still holds an exchange even after it's closed, and the engine references
+            // the associated session object.
             // TODO: https://github.com/project-chip/connectedhomeip/issues/9642
+            ec->SetAutoRequestAck(false);
             ec->SetDelegate(&gFabricCleanupExchangeDelegate);
         }
         else

src/messaging/ExchangeContext.cpp

@@ -317,6 +317,13 @@ bool ExchangeContext::MatchExchange(const SessionHandle & session, const PacketH
 
 void ExchangeContext::OnSessionReleased()
 {
+    if (mFlags.Has(Flags::kFlagClosed))
+    {
+        // Exchange is already being closed. It may occur when closing an exchange after sending
+        // RemoveFabric response which triggers removal of all sessions for the given fabric.
+        return;
+    }
+
     ExchangeHandle ref(*this);
 
     if (IsResponseExpected())