Ok. So we're pretty sure it's not a name resolution issue. I've looked at my installation and there is a built in logger for the online installer. To access these logs open your my documents folder and navigate to XLN Online Installer Logs folder. If there are files there, please open the latest one in Notepad and paste or screenshot the contents to your reply.

If you don't see any files, go to My Documents/XLN Online Installer/Settings. In that folder you should see a file named dont_trace.txt. In order to generate the log, we will rename this to do_trace.txt. After that you want to re-run the installer and let it fail. You should then see a new log file in the location I mentioned earlier and this should shed some light on what is happening in the background. If your Computer name or ID is visible in the first paragraph, please delete it before sharing here.

Matron Landslide
If nothing else it's a learning experience

Quote of the day!!

Anderton

Matron Landslide
If nothing else it's a learning experience

Quote of the day!!

Frustrating experience is probably more to the point! 

abacab

Matron Landslide
If nothing else it's a learning experience

Frustrating experience is probably more to the point! 

Perhaps a link to this post would be relevant? 
What Would Make DAWs (Not Just SONAR) Easier to Use? 

Better plugin installers, and plugins that don't ever crash DAWs, would be a good start...

So ICMP requests and replies are working.  That is a good first step.  However, it does not _totally_ rule out networking, as XLN would be using other ports which could be blocked anywhere.  A Wireshark trace would prove to be helpful here, but not sure if that is something we could do. DNelson's suggestion of posting the log file is the best step forward now.

abacab
Better plugin installers, and plugins that don't ever crash DAWs, would be a good start...

Or a mechanism to sandbox and ID them for resolution without compromising the integrity of the existing project. 

I enabled logging on my XLN online installer, and it appears that it contacts a number of cloud servers. 
 
The log is very verbose, so I just consulted my firewall app to see how many hosts were involved.  I captured some firewall screen info that shows XLN connected with 4 servers.
 

 
On another firewall log I saw that all traffic used HTTPS, so that would be remote port 443.  And this was just the handshake to establish the connection and checking installation to ensure that all of my XLN products were up to date.  Didn't actually need to download any updates.  Everything is up to date.
 
Running XLN Online Installer v1.3.1.

Well I've had nothing but nag screens ever since that XLN update. Now Both computers are doing it.
Opening any project with AD2 warns me I need to log on and authorize my computer, but AD2 runs just fine. 
Only way to get rid of the nag is to run the XLN on line installer which just tells me all is good. I almost think I have to leave it open to get any work done. And this also means I have to stay on line. 
 
Not only that but all of sudden all my Air products are also nagging me and stopped working. I had to update the Pace iLok and it went away.. Is there no peace. At least Sonar is running great. 

One thing that comes to mind with Windows 10 is that the big feature updates/upgrades (Anniversary, Creators, etc.)  seem to alter the computer ID somehow, due to the new Windows build number, or whatever.
 
I had a few plugins need re-authorizing after the last Windows update.  I can't remember which ones they were, but it only affected a few, rather than all of them.
 
I imagine that would depend on how any particular protection scheme involved identifies the computer.  But any time Microsoft updates the build number, it seems to mess with certain plugin authorizations...