Some https website can' t be accessed...

Hi, Since last day afternoon, it' s so strange that some staff cannot access to the https website like the e-banking, webmail via https...etc. This case is happened since last afternoon, the one would keep failed to access to the same https website if he found it' s failed since last afternoon, but some other https websites are working properly~ Even the same https website he can' t be accessed to, other staff may able to access.... so it' s not talking about the issues of the https website... I have no idea now... even both of the DNS server and FG are rebooted, the result is the same~ Anyone could help and give some direction? Thanks!!