Which NSX version do you use? I remember that there are some bugs in the SSL VPN Mac client that were fixed with version 6.3.7 or 6.4.5.
And do you already haved checked the log files on the Mac and Edge Gateway?
We use NSX 6.4.5
The logs on the MAC said the below (I've replace specific info with *):
2019-06-05 16:05:43 INFO Connecting to profile: **** *.*.*.* 443
2019-06-05 16:05:47 INFO Authentication requested by the gateway.
2019-06-05 16:05:54 INFO System Settings are restored.
2019-06-05 16:06:22 ERROR Gateway was unable to authenticate *****
The password is correct as it works on the Windows PC.
There is nothing relevant in the Edge Gateway logs.
Is there any syslog configured for your ESG ??
I found out the problem.
The user concerned had another computer, a Windows computer, already logged into the VPN using the same user account.
As soon as we logged that Windows computer out, the MAC computer could login.
So "Undefined Error" actually means another computer is using your account.