Slow Thin Client after SEP content update

HP t610 thin clients with Windows 7 Embedded. When content updates the devices are down to a crawl and are unusable. Disk activity is 100% and disk queue grows large. 30 minutes later thing go back to normal. Having a hard time receiving help from symantec support for which i have a case open. We have SEP 12.1 RU5 Virus & Spyware protection, Proactive Threat Protection, Network Treat Protection on the devices installed. Thin clients are managed from SEPM with separate policy from all other computers.

Things tried:

1. Disabled scan after definition update-No help

2. Disabled rescan of cache - No Help

Any other suggestions?

Thanks