Hi,
The modular input remains connected and consuming messages from the selected queue/topic while Splunk is running. So, once Splunk is started, the consumer should remain connected to ActiveMQ forever. At least for now, the modular input does not reconnect to ActiveMQ/RabbitMQ/whatever if the connection fails, but I don't think that's your problem. Have you checked the ActiveMQ console to check if you can see the incoming connection from Splunk?
Today we have released a new version of the module (v0.4). It adds some extra configuration option and other minor changes. It's not related with your issue, but you can also try to update to the latest version.
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