Seen in rls2404 coverage job. Packet trace [0] sees mtu:9000 in ip4-rewrite, not sure why exactly yet. Maybe CSIT test forgets to set higher value somewhere, maybe VPP code inserts 9000 by default as here [1]. The fact fragments cannot be longer that one buffer is a known limitation.

[0] https://s3-logs.fd.io/vex-yul-rot-jenkins-1/csit-vpp-perf-report-coverage-2402-2n-clx/21/log.html.gz#s1-s1-s1-s1-s2-t6-k3-k7-k1-k1-k1-k8-k14-k2-k1-k1-k1-k1
[1] https://github.com/FDio/vpp/blob/455960759b5417c767ed331748c7ee76662ffd18/src/vnet/interface_funcs.h#L323