FortiClient VPN on iPad got errors with 'Insufficient credential' and 'Unable to connect'

[soba]

We're currently using a FortiGate 201E (v7.2.12), and encountering an issue with FortiClient VPN-only version 7.4.10.0196 on iPad.

When connecting:

• Repeated "Insufficient credential" error, even with valid 2FA token
  
• Eventually shows "Unable to connect", VPN session ends
• After multiple retries, VPN connects successfully

Issue only occurs on iPad, not Windows or Android.

Looking for any insight or similar experience — would appreciate any help!

[soba]

Here is 'Unable to connect' error page.

[soba]

We found that on LTE/5G mobile networks, the public IP address can change randomly (sometimes within minutes, sometimes within seconds).

Because of this, the source IP at the start of the login session could be different from the source IP when entering the email 2FA code, so FortiGate treated it as a session mismatch and blocked the login.

This did not happen on Wi-Fi because the IP address was stable.

The issue was fixed by disabling the source IP check:

'config vpn ssl settings'

-> 'set auth-session-check-source-ip disable'.