I see your question has gone unanswered and I will try to give you a meaningful answer to your query, though I suspect after 9 days you may have self-resolved your issue.
Once you have added an agent node to LEM, you need to enable connectors for each node.
Select the node > click the gear icon > Connectors.
Find a connector (you can refine the results shown using the search function.
Click the gear icon next to a connector > New.
Check the connector values. Pay attention to the output method and select the desired type (you can change this later if necessary). Alert will only send to the alerts and not be logged. Send to nDepth and you will be able to perform search queries and reports on events. Select both for full functionality.
Click Save then click the cog icon again and Start to start the connector.
The connector will now begin to poll the relevant log on the node and forward these events to LEM. If for example this log is a Windows log, ensure that events are being generated on the node to confirm the connector is configured as expected.
I hope that this helps.
Garreth's advice is helpful here. Agents still connected, still configured? Event logs aren't full if you're monitoring event logs? License hasn't expired (that will also stop data from coming in)?
I have seen this myself on a new install of LEM 5.6.0 using the desktop console and web console. It only occurs the first time I log in to the appliance. Once I logout, close the console application/browser and login again, the events are displayed in the monitor window. I was able to prove events were being received by using nDepth to return all events within the last 10 minutes and re-run the query periodically. Also, I could see metrics gathered in the Ops Center relating to new events received to the appliance.
Hope this helps.