This was previously mentioned as a secondary symptom of CSIT-1800. But that ticket is mostly about VPP crashes (not seen recently), while this symptom (NDRPDR failure but no crash) still can [0] happen, albeit rarely. Interestingly, all tests within the suite failed the same way.
No clear relation to number of tunnels is visible yet.
More investigation needed for proper VPP bug-report.

[0] https://s3-logs.fd.io/vex-yul-rot-jenkins-1/csit-vpp-perf-report-iterative-2406-2n-zn2/54/log.html.gz#s1-s1-s1-s3-s1-t1-k2-k9-k14