Session login stalls just before "Validating Session Cookie"

[codewize]

This is a configuration with hundreds of users successful using this system so the issue is not in my config.
I have a group of users all form the same company using Anyconnect 4.8.xxxx

There were able to log in and use the system successfully for a couple of weeks, then something changed.
Now, when they try to log in, debug shows they get the banner, they click OK then it hangs with the last line in the debug being the 
webvpn_svc_parse_acl: after add: etc etc etc

I am able to log in with the same credentials without issue so this is client related, but what is it?

The debug for a good login goes form that line to Validating Session Cookie, then continues on.

So what is preventing them from getting to the 

[Marvin Rhoads]

Wild guess but have you checked the system time on the clients with the problem? If they are all pointing to an incorrect ntp (or DC or wherever they get their system time) and it is incorrect or invalid that may cause the behavior you are seeing.

[codewize]

Interesting, thought. No I have not but I do know they are in a different time zone, which was not a problem previously but let me ask them to verify client times.

[codewize]

Time has been confirmed as accurate on the clients