This article explains how the dlu.ucode.not_routable trapcode is observed on hop routers due to Interface Flaps.

•  Interface flap event triggers label change/delete on the transit routers resulting in traffic loss.
• LSR router in the path deletes LSP and the label information and as a result, if the router receives a packet with old label information, it does not know where to route that traffic.
• So, it drops it and increments ‘dlu.ucode.not_routable’ trapcode.

Troubleshooting:

1. Across the LSP, check if there are any flapping interfaces. If yes, then disable the interface to mitigate the issue.
2. Dump the trapcodes so that we can decode them later.
3. Identify the LSP dropping traffic by tracing the label from transit router dropping traffic.
4. Once this LSP is identified, manually clear the LSP once to re-signal using below command. On ingress LER node, please issue below cli command: clear mpls lsp name <LSP name>
5. This will force the LSP to find an alternative path through the network towards the egress router.

If the issue persits then please reach out to the RE/CFTS team for further troubleshooting.