Hi again,
I found the reason, As you know when using Hotspot service, it creates dynamic Filter and NAT rules. One of them is:
14 D chain=hs-unauth action=redirect to-ports=64875 protocol=tcp dst-port=443
So some applications (maybe bad applications) installed on user PC tries to establish HTTPS connection every moment and RouterOS redirects all those requests to port 64875 (hotspot login page). Therefor CPU usage increases 100%. When user logged in, it stops. Or when I remove this NAT rule, it stops. But without this rule, can`t redirect HTTPS request to login page.
Now I removed this dynamic rule (because can`t change dynamic rules) and added new one like that but changed connection limit:
chain=hs-unauth action=redirect to-ports=64875 protocol=tcp dst-port=443 connection-limit=10,32
Now I`m waiting users, who was affected to network. Because yesterday when I changed NAT rule, bad user turned off his computer. I hope it will work.