Problem creating NFS SPN on a TrueNAS Core

I’m trying to setup an NFSv4 with Kerberos. I’m using a Samba4 AD which is joined successfully and samba shares work. I also want to setup an NFSv4 share but my problem is that whenever I try to add an NFS SPN using the same admin/password used for joining the AD I get this:

Error
[EFAULT] failed to set spn entry [nfs]: Processing principals to add...
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Error: Traceback (most recent call last):
  File "/usr/local/lib/python3.9/site-packages/middlewared/main.py", line 139, in call_method
    result = await self.middleware._call(message['method'], serviceobj, methodobj, params, app=self)
  File "/usr/local/lib/python3.9/site-packages/middlewared/main.py", line 1240, in _call
    return await methodobj(*prepared_call.args)
  File "/usr/local/lib/python3.9/site-packages/middlewared/schema.py", line 981, in nf
    return await f(*args, **kwargs)
  File "/usr/local/lib/python3.9/site-packages/middlewared/plugins/nfs_/krb5.py", line 91, in add_principal
    ret = await self.add_principal_ad(data)
  File "/usr/local/lib/python3.9/site-packages/middlewared/plugins/nfs_/krb5.py", line 52, in add_principal_ad
    return await self.middleware.call('activedirectory.add_nfs_spn', ad)
  File "/usr/local/lib/python3.9/site-packages/middlewared/main.py", line 1283, in call
    return await self._call(
  File "/usr/local/lib/python3.9/site-packages/middlewared/main.py", line 1240, in _call
    return await methodobj(*prepared_call.args)
  File "/usr/local/lib/python3.9/site-packages/middlewared/plugins/activedirectory.py", line 1165, in add_nfs_spn
    ok = await self.net_keytab_add_update_ads('nfs')
  File "/usr/local/lib/python3.9/site-packages/middlewared/plugins/activedirectory.py", line 1105, in net_keytab_add_update_ads
    raise CallError('failed to set spn entry '
middlewared.service_exception.CallError: [EFAULT] failed to set spn entry [nfs]: Processing principals to add...

Any idea how I can debug this problem? Thanks