These articles do not appear to pertain to my issue. Mostly they about network lag, which I do not have on any of the many devices in our home. Also network lag does not occur like clockwork - every 73 seconds. I find nothing in the other articles that either I haven't tried or that's pertinent.
That said it is related to network activity and I did some more testing.
To see if it was related to the Ethernet adaptor and connection to the router I disconnected the Ethernet cable and enabled WiFi. The same glitch occurs on WiFi. I know that the modem/router can't be the culprit because none of the other many streaming and other network dependent devices are having any issues. And I've rebooted that modem/router several times between the time this started and now.
When this glitch occurs, using TM, I can see that there is network traffic that starts and ends with the freeze. My guess is whatever process is generating the traffic is somehow getting exclusive use of the Windows process that sends and receives network traffic and blocking any other process from using it. This process sits above the driver level since it affects both the Wifi and Ethernet traffic. Most apps aren't really affected by this as a continuous stream is not required, there is application buffering etc that shields them from being interrupted by temporarily not having access to the network. But these flight sim apps,, when they are configured to use the network, do depend on continuous access.
Also remember that this happens even when all startup apps are disabled, and all non-MS services are disabled. So it has to be an MS process of some sort that is getting kicked off every 73 seconds. Why this has started recently I cannot hazard a guess. I don't remember if or when I made any changes to the system around the time this started happening.
Something else interesting. I had a third party service, RTSS Rivatuner, that started up with Windows. When I was using Process Explorer to try to see what was going on, I was looking at the comings and goings of dllhost.exe instances. When the freeze happened, a dllshost.exe instance was initiated with a RTSS server footprint. It's in one of the reports on the Google Drive. My guess is that ordinarily that process would come and go so quickly that it wouldn't be noticed. But when the network was blocked, it was hung, waiting for network access to resume. It also looks like under some conditions that process is doing some sort of exclusive send, as the receive traffic drops off when this happens.
Is there a way of getting more help on this from Microsoft? In all the searching both you and I have done we haven't seen anything that explains this behavior so it must be very rare. It might require doing a network or system trace. Anyway - looking for ideas. Thanks.