So let me understand this clearly, you have pushed 1000 routes and then noticed that you have a high CPU load, then after sometime the CPU load went back to normal [can you tell me how much time it took?], did you try pushing more routes afterwards? Or you just restarted the service?
We think your pushing the SMB appliance to its limits here by the number of routes your entering, which is clearly why the CPU load is rising.
Waiting for some clarification from your side, since if after pushing the routes and waiting for some time the CPU load is normal then clearly the issue was adding the routes.