Fortinet is still researching, but in the meantime it appears this issue
is limited to sites that have "mediocre" SSL certificates. Sha1 signed
certs cause the problem in Chrome, but work Okay in IE11. TLS 1.0/1.1
(not TLS 1.2 capable) and/or the RC4...
I also have the same issue on 5.4.1, except a little worse; any site,
not on the SSL inspection bypass list, will give this error and there is
no workaround except for turning SSL inspection off for that policy. I
have created a ticket with Fortinet ...
