These are inventory files sent by the agents, to the scalability server. Is the same happening for all SS, or only one of them?
These files get collected by an Engine on the DM. You mention you have (4) SS, so you should have (5) Collect Tasks running on the DM. One for the DM's own built-in scalability server, and four more for each remote scalability server.
So what are the status of these collect tasks on the engine?
Are all (5) collect tasks linked to an engine?
What are the status and last run dates?
In the activity window of the engine, you should see files getting processed.