NPM Interface Downtime

I have 2 Cisco Switches which is "indirectly" connected via Remote Optical Network.

Both Interfaces are reflected as "Line Up, Protocol Up" on the console view.

Setup

Switch 1 <----- dark fibre -----> Switch 2

However from "Interface Downtime" view, only Switch 1 shows interface as up, while another endpoint Switch 2 still shows as down.

But on the interface view of Switch 2, the "Interface Detail" Status however is reflected as "Up". Just that "Interface Downtime" still shows as down.

Any idea how NPM or what data NPM uses to poll the data?