Most recently, it seems that our older N4100 units encounter issues where clients instead of redirected to the captive portal are prompted with warning message that the connection is not secure.
This is due to the redirect being set to IP address 220.127.116.11 back then, which by now is reserved for the Cloudflare DNS server.
The solution to this issue is, to either create yourself a certificate according to the SOP guide (requires Linux machine) attached to this article.
For customers who do not have this option, we have already created a certificate that can be implemented, which is also linked to this article.
Private key of the certificate is 12345
Private Key File = private.key
Certificate File = Certificate.crt
You also need to set the SSL login page enabled on the N4100, screenshot below: