When accessing https://mcgillcrm.com some users are seeing this in chrome: ERR_SSL_PROTOCOL and this is firefox: SSL_ERROR_RX_RECORD_TOO_LONG
But it only happens when they access the site through a specific ISP (Videotron).
When the site is accessed via a hotspot or when connected to a different ISP it works fine and it also works if the user is using Windows machine instead of a Mac.
I verified SSL labs, checked port 443 and compared against another site where it doesn’t throw this error and everything seems fine.
We have a 301 redirect towards https and I double checked that users really type https:// when accessing the web-site, but it still doesn’t work.