This issue appeared recently when a client needed to access the ARCGIS web site at https://www.arcgis.com/index.html . When tested from another site using a Sophos Cyberoam UTM – the same software release as this client – the same problem was observed and the site would not load fully.
That version had a number of fixes
CLITE-1055 Resolved vulnerability related to TCP SACK PANIC
CLITE-1063 Addressed an issue allowing a fake server to use WINGc to create arbitrary files
CLITE-1045 Resolved an issue with the antivirus service not starting with reported scenario (old default AV engine)
CLITE-937 Resolved an issue stopping the antivirus service when the service starts from the GUI
CLITE-418 Extended the support of the Cipher Suite for TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (0xc02f)