On iOS 11.3, when the end user is attempting to authenticate with Duo Push from Duo Security or Microsoft Azure with 2-way SMS via Pulse Mobile for iOS, authentication will fail with the following error:
Connecting Error
The server is not responding
Screenshot:

This issue occurs when all of the following conditions are met:
- Pulse Mobile for iOS is running on iOS 11.3 and above. (This issue does not impact Pulse Mobile running on iOS 11.2 and below OR Pulse Mobile for Android.
- During authentication, the end user has to switch between Pulse Mobile and the third-party vendor MFA application to accept the MFA response.
Authentication scenarios that are impacted:
- Using Duo Push from Duo Security
- Microsoft Azure MFA with 2-way SMS
Authentication scenarios that are not impacted:
- Using Phone Call mechanism from Duo Security
- Google Authenticator integration with Pulse Connect Secure
- Any MFA solution that sends a challenge to the PCS / PPS device where the end user receives a one-time password (OTP) prompt (similar to classic version of RSA, etc)
Pulse Secure will continue to update this article with additional authentication scenarios as they are confirmed.