DNFS is not working on ODA X7-2 with Oracle 12.2.0.1

After we switched to ODA X7-2 HA with Oracle 12.2.0.1, the DNFS has stopped working, even though DNFS is enabled by default in 12.2. (It was working in 11g)

Based on the documentation, I'm using insecure parameter in the /etc/exports file. 

/nfs_backup     oda1(rw,no_root_squash,insecure,anonuid=1001,anongid=1001)

/etc/fstab entry is as follows:

oda-nfsserver:/nfs_backup           /nfs_backup    nfs     rw   0 0

However, when exporting to the DNFS mount, the export ends with multiple errors:

[oracle@oda1 scripts]$ expdp \'/ as sysdba\' directory=dumps dumpfile=test.dmp logfile=test.log tables=ams.employee reuse_dumpfiles=yes

Export: Release 12.2.0.1.0 - Production on Wed May 6 10:56:33 2020