A confident system administrator will always try to debug the issue, not just check logs. Add something like the following to your named.conf, then monitor the logs:
logging {
category "update" { "debug"; };
category "queries" { "debug"; };
category "dispatch" { "debug"; };
channel "debug" {
file "/var/log/named.log" versions 2 size 50m;
print-time yes;
print-category yes;
};
Of course you should modify the example above to make it more relevant to your issue, not just copy & paste.