BIND 9.18 unable to successfully transfer zone from axfrdns primary

[Ian Bobbitt]

I have a system running BIND 9.18.17 that needs to transfer a zone from 
djbdns/axfrdns. I receive FORMERRs, and haven't been able to get any log 
messages indicating the problem.

xfer-in: info: zone example.net/IN: Transfer started.
xfer-in: info: transfer of 'example.net/IN' from 198.51.100.1#53: 
connected using 192.0.2.1#53
xfer-in: error: transfer of 'example.net/IN' from 198.51.100.1#53: 
failed while receiving responses: FORMERR
xfer-in: info: transfer of 'example.net/IN' from 198.51.100.1#53: 
Transfer status: FORMERR
xfer-in: info: transfer of 'example.net/IN' from 198.51.100.1#53: 
Transfer completed: 0 messages, 0 records, 0 bytes, 0.008 secs (0 
bytes/sec) (serial 0)

This replaced a long obsolete system running 9.8.2 that was able to 
successfully transfer the zone. I can also successfully transfer the 
zone with `dig -t axfr ...` from the new system, which gives no errors. 
named-checkzone on the resulting data also gives no errors, and BIND is 
able to successfully load it as a primary.

How do I go about finding the cause of the FORMERR and resolve it?

-- Ian