IWe recently upgraded everyone in my facility and in my company's Mexico facility to SW 2015 SP3 from SW2014 SP5. We used an admin image to roll this out.   The roll out seemed to go smoothly except we have 1 user in my location and 1 user in a Mexico location reporting that they can open Solidworks and work for some time but then they get a pop up saying

"Could not obtain a network license for the following product(s):
SOLIDWORKS standard

Please check your network connection to the license server and that the license server is running."

There doesn't seem to me to be any rhyme or reason why they would get this error.  Here is a list of some other info about the environment and the issue.

1. There is an SNL in each location servicing that location.   The Mexico user connects to the Mexico SNL,  The USA user connects to the USA SNL.

2. This didn't happen with either user in SW 2014

3. The license server in either location has not reached its user limit at any of the times the user has reported the error   (in fact we haven't hit our limit at all in the last month worth of logs that I have on hand)

4. we do have a 30 minute timeout in the Options file but the error does not correspond to that either.  In fact sometimes the error happens within the first 15-20 minutes of use before the timeout could ever be invoked.

5. I have reviewed the event viewer logs for each computer and cannot see where there was any type of network disruption for the user.  The user also hasn't reported that their email has become disconnected from Exchange, network drives closing etc....none of the normal items we see when the network is disconnected or a switch goes down in our environment

6. This happens whether wired or wireless.   One user is wired only, and the other user has a laptop and has seen the error in both instances.

7.  I have done a complete uninstall of SW on the USA user,   registry scrub etc and then re-installed the admin image.

8.  I have sent the log file to my VAR to look over but they could not find any glaring discrepancies.  They only mentioned the timeout entries in the log but noted that they didnt correspond to any of the user's errors.

9.  When the user has sent screenshots with a timestamp I have been able to look at the log and see where a license was checked back in at that same time and a license was checked back out 4 or 5 seconds later.

10.  No other user accessing the same SNL with the same admin image has reported the issue.

What else do should I be looking at in trying to troubleshoot this issue?