It sounds like you have NMIS configured to run in Classic mode. We strongly suggest you change this to Fine-Grain, which will differentiate between a degraded device and a full device down. Select Setup->Basic Setup from the NMIS menu, then change Node Status Mode, and click Save Settings before closing the window.
You can read more about the Node Status options, how they work, and what they change, on our wiki, HERE: https://community.opmantek.com/display/NMIS/NMIS+Node+Status
It sounds like you've created your own system to handle copying device data from pollers to a master server. We have a module that does that now and creates multiple layers of debug information, as well as handles multiple masters, high availability, D&R and device deduplification at the master.
In order to help you debug your code we would need to have a NMIS Support & Maintenance agreement in place, as well as a Development Support contract. Please contact us at email@example.com if you would like to discuss this further.
i made configuration change as you advised but still has not changed. i also looked at wiki link all looks to be fine. we have slave server that is still running the nmis8.5.6. master server operates fine besides the ghost down node i'm battling to find. any tshoot tip that i can try out?