Apologies for the inconvenience, This issue has been reported to Intel IT team.
Once we hear back from Intel Internal team about this issue, we will let you know.
Please till then check with different browsers like Chrome, IE etc.
Now I could able to download the Quartus 18.1 Lite edition, since issue might have fixed. Please check at your end or else you can download Quartus 18.0 Lite from below old thread,