Gad!  You need to get a working firewall, Carlos!  You've got
NFS open to the broad Internet, including mountd!  What
could possibly go wrong?

The machine runs SuSEfirewall2, which is open to the intranet. It is not aware that IPv6 is internet and doesn't close it. I can change to firewalld, but I don't know if it is better in this respect, or how to coach it.

And the router firewall is faulty.