Could you check if Application Signature package is updated on the controller.
Go to SZ GUI >> Firewall >> Application control >> Check the application signature package file name.
There could be other factors as well like issue in the network, Port blocked between the AP-SZ, etc.
Make sure port 22 and 443 are open between the AP-SZ.
Syamantak Omer | Community moderator | Staff TSE | CWNA | CCNA | RASZA | RICXI | Follow me at https://linkedin.com/in/syamantak-omer-5949b6124