Update:
I changed web server to Apache/2.4.38 + mod_php.
But unfortunately the issue was exactly same as Nginx + php-fpm.
shortly summarize the issue was:
Invalid CSRF Token CSRFToken
Invalid CSRF token while assigned ticket
then
all agent's email reply become invalid:
Ticket rejected (foo@bar.net) (unregistered client)
it should be bug. I would like to try 1.10 again.