How to handle exceptions from using request reply router in mule - mule

Question

I am using the following fork and join pattern in my flow.Parallel processing works just fine. However, I have issues with exception handling. I want to implement an exception strategy for the processing happening on VM response inbound endpoint of the router. However, it seems my nothing happens when I am trying to write to response, from within the catch exception strategy block. When there is an exception, I am able to see the log statement from the catch block, but the response on browser just hangs.
Please suggest.
<flow name="forkAndJoinFlow" doc:name="forkAndJoinFlow">
<http:inbound-endpoint exchange-pattern="request-response" host="localhost" port="81" path="lowestprice" doc:name="HTTP"/>
<not-filter doc:name="Not">
<wildcard-filter pattern="*favicon*" caseSensitive="true"/>
</not-filter>
<request-reply>
<all>
<vm:outbound-endpoint path="shop1"/>
<vm:outbound-endpoint path="shop2"/>
</all>
<vm:inbound-endpoint path="response">
<message-properties-transformer>
<add-message-property key="MULE_CORRELATION_GROUP_SIZE" value="2" />
</message-properties-transformer>
<collection-aggregator />
</vm:inbound-endpoint>
</request-reply>
<expression-transformer evaluator="groovy" expression="java.util.Collections.min(payload)" doc:name="Expression"/>
<object-to-string-transformer doc:name="Object to String"/>
<logger level="WARN" message="#[string:Lowest price: #[payload]]" doc:name="Logger"/>
<catch-exception-strategy doc:name="Catch Exception Strategy">
<logger message="EXCEPTION:#[payload]" level="INFO" doc:name="Logger"></logger>
<!--Nothing happens after this-->
<object-to-string-transformer doc:name="Object to String"></object-to-string-transformer></catch-exception-strategy>
</flow>
<flow name="shop1Flow" doc:name="shop1Flow">
<vm:inbound-endpoint path="shop1" doc:name="VM"/>
<logger level="INFO" message="SHOP1 Flow..." doc:name="Logger"/>
<expression-transformer evaluator="groovy" expression="new java.lang.Double(1000.0 * Math.random()).intValue()" doc:name="Expression"/>
<logger level="WARN" message="#[string:Price from shop 1: #[payload]]" doc:name="Logger"/>
</flow>
<flow name="shop2Flow" doc:name="shop2Flow">
<vm:inbound-endpoint path="shop2" doc:name="VM"/>
<logger level="INFO" message="SHOP2 Flow..." doc:name="Logger"/>
<expression-transformer evaluator="groovy" expression="new java.lang.Double(1000.0 * Math.random()).intValue()" doc:name="Expression"/>
<logger level="WARN" message="#[string:Price from shop 2: #[payload]]" doc:name="Logger"/>`enter code here`
</flow>
</mule>