What OPC server are you using? It appears that FactorySQL is working, but that the OPC server is not publishing data. By restarting groups/FactorySQL, you are resubscribing the items and getting them to work again.
Knowing which OPC server you’re using will help us troubleshoot. If it happens to be RSLinx, we’ve seen problems in the past with data updates stopping under high load (which could happen on startup). Going into FactorySQL>Settings>Service Settings and setting the “OPC Update Rate %” to “100%” can reduce the load on the OPC server and was shown to help in those cases with RSLinx. For historical logging, setting that value to 100% is fine.
Regards,