ConnectX-5 25GbE missing RDMA devices

On a Ubuntu 20.04 system we have a ConnectX-5 dual port 25GbE adapter (MCX512F-ACAT). tcp Communication over a port of this card is possible, but we see no rdma device.

# ibv_devinfo
No IB devices found

system: Ubuntu 20.04.4
kernel 5.4.0-100-generic (5.4.0-126-generic also tested)
MOFED 5.4-3.5.8.0-ubuntu20.04
adapter FW: 16.34.1002

on boot we see some messages, which we do not have on other nodes:

[ 2794.490435] infiniband mlx5_0: mlx5_ib_test_wc:392:(pid 1000939): Error -110 while trying to test write-combining support
[ 2794.700217] mlx5_ib.rdma: probe of mlx5_core.rdma.0 failed with error -12

thanks for any idea, Ralf