The devices you mentioned all detect captive portals differently. For instance, iOS devices check for reachability to apple.com, captive.apple.com, and a few other FQDNs. If those sites are accessible, the Apple Captive Network Assist is not displayed on the device. A common method for preventing the CNA from coming up is to whitelist the FQDNs mentioned. This can be accomplished by adding a whitelist to the captive portal profile or giving the guest logon role access to those FQDNs. Is it possible that you or another network admin made such a change?