I have done as you'd said and it helped me. But I've got the other problem - Purview appliance is on and "green" in Devices, but it says: "Sensor is down"
Ilya, you may want to open a case.
It sounds like the Netsight server is likely running low on resources.
It is best to check the following to start, to make sure you are within these guidlines, especially if running version 8.x