Symantec AV with cDOT general advice

Hi, we are running Symantec Protection Engine : Version 7.5.1.5 on netapp cDOT 8.3.1. - mandatory scan off

I haven't been hugely impressed as scanners appear to randomly drop off our SVMs.

eg SVMA on Cluster1 lost 4 of 5 scanners causing huge latency. The other SVM's on Cluster1 not affected.

All the SVMs use  the cluster management LIFS. I don't see disconnects in the logs.  

Does anyone else use Symantec AV?  

Given the random issues can anyone recommend any other solutions?

I'd prefer not using any AV with Netapp.

thanks Rob