No A or AAAA record for NS (Reverse DNS)

Strange - copy and pasting your answer and running named-checkzone on it results in:

acshellam@dev1:/tmp$ named-checkzone example.com example.com.zone
zone example.com/IN: loaded serial 12
OK

acshellam@dev1:/tmp$ named-checkzone -v
9.6.1-P2

You sure that's the correct zone file you have on your system? Is there an $ORIGIN directive somewhere between the NS and the A records in your file that's changing the zone root?

I've been caught on this before.

You can't check the reverse zone file with the same domain because you need to use the reverse domain.

Try the following:

named-checkzone 1.168.192.in-addr.arpa <reverse zone file>