VXLAN offloading not working with Mellanox/CX5 & Kernel 6.1

OS installation is standard Debian 12
Booting with kernel 5.10 everything works.

  • All cores are almost idle
  • TCP packet size for iperf traffic is 65160 bytes
  • Debug FS is present
    Booting with kernel 6.1 offloading does not work.
  • One core at 100 % work
  • TCP packet size for iperf traffic is 15928 bytes sometimes 65160
  • Debug filesystem does not show the VXLAN offloading at all
root@box:~# ls /sys/kernel/debug/mlx5/0000:04:00.1/eth1/VXLAN
ls: cannot access '/sys/kernel/debug/mlx5/0000:04:00.1/eth1/VXLAN': No such file or directory
root@box:~# ls /sys/kernel/debug/mlx5/0000:04:00.1/VXLAN
ls: cannot access '/sys/kernel/debug/mlx5/0000:04:00.0/VXLAN': No such file or directory

Strangely ethtool still reports that things are working with kernel 6.1

root@box:~# ethtool -k eth1 | grep udp_tnl
tx-udp_tnl-segmentation: on
tx-udp_tnl-csum-segmentation: on
root@box:~# ethtool -k eth1 | grep rx-udp_tunnel-port-offload
rx-udp_tunnel-port-offload: on

All tests done according to:
https://docs.nvidia.com/networking/display/mlnxofedv23101190lts/vxlan+hardware+stateless+offloads
Offloading definitely should work, it does not. There are no error log lines.
Has the configuration changed? How to fix this?