Cannot set RX flow hash configuration: Operation not supported

I have problems with my SMB multichannel setup and found out that windows supports the toeplitz hash function that needs a key length of 40 Bytes and some websites claim that XOR is supported as well. So I checked the RSS configuration of my network adapter:

ethtool -x eth0
RX flow hash indirection table for eth0 with 4 RX ring(s):
    0:      0     1     2     3     0     1     2     3
    8:      0     1     2     3     0     1     2     3
   16:      0     1     2     3     0     1     2     3
   24:      0     1     2     3     0     1     2     3
   32:      0     1     2     3     0     1     2     3
   40:      0     1     2     3     0     1     2     3
   48:      0     1     2     3     0     1     2     3
   56:      0     1     2     3     0     1     2     3
RSS hash key:
1e:ad:71:87:65:fc:26:7d:0d:45:67:74:cd:06:1a:18:b6:c1:f0:c7:bb:18:be:f8:19:13:4b:a9:d0:3e:fe:70:25:03:ab:50:6a:8b:82:0c
RSS hash function:
    toeplitz: on
    xor: off
    crc32: off

As you can see "toeplitz" is active and the key has a length of 40 bytes (hexadecimal). Should be correct. But I wanted to test if my problems will be solved if I enable XOR, but it fails:

# ethtool -X eth0 hfunc xor
Cannot set RX flow hash configuration: Operation not supported

Then I tried to overwrite the key (with the same value), but this fails, too:

# ethtool -X eth0 hkey 1e:ad:71:87:65:fc:26:7d:0d:45:67:74:cd:06:1a:18:b6:c1:f0:c7:bb:18:be:f8:19:13:4b:a9:d0:3e:fe:70:25:03:ab:50:6a:8b:82:0c
Cannot set RX flow hash configuration: Operation not supported

Finally I tried to allow XOR on an onboard NIC:

ethtool -X eth1 hfunc xor
Killed

After that http://tower/Settings/NetworkSettings isn't loaded anymore and the CPU has maximum load:

Then I tried to reboot the server, but it seems to be frozen as I'm still able to access through SMB (?) while the webclient is dead, external ssh is dead (putty) and the terminal hangs at "Starting diagnostics collection...

After pressing the powerbutton the shutdown process repeated. But finally hanged again on "Starting diagnostics collection..." so I needed to hold the powerbutton to force shutdown.

I'm not sure if this is a bug related to Unraid, Slackware or the network adapter, but it seems to be a bug as all search engine results are related to bugs.