Horizon/Duo Redirect Issues

[niaboc]

When logging into Horizon, external users are getting stuck on a Horizon/Duo redirect page.  It does this for the Horizon client and thin clients.  VMware support is saying it is a time sync issue.  When I changed the time zone on the UAG, the issues went away for a few days then returned.  If I disable SAML auth on the UAG, external users are able to connect without the Duo prompt.  Has anyone seen this issue before? 

[DuoKristina]

I have no experience with UAG.

>external users are getting stuck on a Horizon/Duo redirect page

Can you say more about this? Is this UAG trying to redirect to Duo SSO primary login? Is this Duo SSO trying to redirect back to UAG after someone completes primary auth and 2FA in Duo SSO? Does "stuck" mean it's looping?