One suggestion...
When the APs are all connected on 9.6, from Configure::Access Points, AP Policies, check the
Limited ZD Discovery box and enter your ZD IP address.
Upgrading the ZD should not cause your APs to change IP address, so after the upgrade, see if
you can ping the disconnected AP(s). If so, can you SSH to them, login with ZD admin credentials,
and issue a 'set director ip a.b.c.d' with your ZD's IP, then 'reboot'?
This will tell the APs to send LWAPP to your ZD's IP address when they come up again. If they
all connected under 9.6, I think they should all reconnect on 9.8.2 as well.