Recently we have had a few support cases where a customer was unable to log in to the firewall via WebUI after the firmware update. But SSH access worked fine.
It turned out that during the update process the server certificate used for the WebUI is lost.
Config with v6.0.4 (it does not happen with «self-signed» only):
config system global
set admin-server-cert "self-signed"
Config after update to 6.2.0:
config system global set admin-server-cert "" end
Unfortunately we do not exactly know in which situation the problem occur (specific certificates, only? which firmware versions?). But if you notice the situation that you cannot access the WebUI with https but ssh is working, then it’s worth to check the setting for the admin-server-cert.
In case there is no admin-server-cert choosen, just set it again.
Apparently, the problem also occurs when upgrading to 6.0.8.