Zone transfer is happening intermittently between slave and master bind

[Chuck Aurora]

My guess comes from a hint in Tony's post,

On 2021-03-17 07:51, Tony Finch wrote:
> 17-Mar-2021 12:36:28.812 general: info: zone cam.ac.uk/IN/main:
> 	notify from 2001:630:212:8::d:aa#43432: serial 1615984588

> 17-Mar-2021 12:20:36.985 general: info: zone cl.cam.ac.uk/IN/main:
> 	notify from 128.232.0.19#44340: zone is up to date
> 
> If the log messages do not match up like this then something isn't 
> working
> properly, such as the allow-notify ACL on the secondary - check there
> aren't any erroneous "refused notify from..." messages in the 
> secondary's
> logs.

My guess is that you are dual-stack but have not fully configured the
ipv6 side of things; maybe need to expand your masters {} list and
allow-transfer and allow-notify to include both protocol addresses?

[Exactly the situation I am in today, after enabling v6 on my second of
3 NS hosts.  Just a thought.]