There is an announcement on the support portal but minimal to no issue with ZD platforms until 10.x is released so its more about being aware before upgrade.
With regards to SZ platform the AP will be unable to maintain a session to the controller if the cert is out of date. This will render the AP useless. If you have the latest version of firmware installed then there is a new form for AP cert checks and the SZ will list all the APs that are connected to the SZ that require a cert update.
The form is also present in latest versions of ZD firmware so you certainly should see it in the ZD1200 GUI