GUI session lost after importing CA certificate

Hi Everyone,

Hope you guys can help with this issue.

Today, I imported a new CA certificate at D300 and lost GUI connection.

I can access the firewall through putty so it is online.

Please see the detail I found. I can see set admin-server-cert " " there is no certificate on it.

Compared with another firewall and I  can see it is self-sign added.

Please share if anyone has any ideas or suggestions. Thanks in advance!!

******* # sh sys glo
config system global
set admin-https-ssl-versions tlsv1-2
set admin-server-cert ''
set admin-sport 443
set admintimeout 20
set alias "**************"
set hostname "********"
set ldapconntimeout 1000
set log-uuid-address enable
set proxy-auth-timeout 5
set timezone 65
set wifi-ca-certificate "Fortinet_CA"
set wifi-certificate ''