Hi Alexey,
What type of SSID the client is connected to? Is it a Radius SSID?
Is this happening with any particular AP model\Client model?
We need to understand where the client is failing, can you confirm if the clients are failing to authenticate or passing the association\authentication but fails to obtain the IP address?
I see that the issue happened on Nov 22nd, are you still facing the issue?
Regards,
Sanjay Kumar