I am not 100% sure how to tell. I assumed from my investigations that this iOS11 issue was a captive portal issue, especially after going into the 'Security' settings and noticing that we HAD one (called 'default').
According to the settings for the wireless SSID in question...
1) WLAN Settings
Primary usage: Employee
2) VLAN
Client IP assignment: Network assigned
Client VLAN assignment: Default
3) Security
Key management: WPA-2 Enterprise
Authentication Server 1: InternalServer
Rauth interval: 0 hrs
There are a bunch of unchecked boxes. There is the 'default certificate' for the internal service and an 'upload certificate' button where I could, I realize now, upload my new certificate?
None of the 802.11 boxes are checked
4) Access
Unrestricted
Is that enough for you to go on? If you need more information, please let me know. Thank you so much for helping me with this, I really appreciate it!!