It appears I discovered the source of my problem, and hopefully it helps others.
I found a setting in my Linksys router (model EA7500 with firmware version 1.1.5.190349) called Media Prioritization which was turned on. I know this performs traffic blocking and bandwidth limiting to favor other devices on the network, so I turned this off while the Flight Simulator download was running. As soon as I saved the setting in the router, the looping stopped, and the downloads of the large files went to 100%. After more than 2 weeks of troubleshooting, I can’t believe it was this simple setting.
This also explains why slowing down the download speed with NetLimiter 4 helped before I turned off that feature - I wasn’t using as much bandwidth, so it was much less likely to be limited by the router. With Media Prioritization turned off in my router, I was also able to turn off NetLimiter 4, and download at full speed with no download loops/resets. So nice to not see it going back to 0% over and over!!!
For others having the same problem, I’d love to hear if you find a similar issue on your own routers. If we can confirm this helps others, I’ll update the ZenDesk support case I have open with the additional info, and maybe it will help the developers accommodate such connection resets within the Flight Simulator downloader/installer.
Best wishes to all you patient people who waited this long to find a solution as I have! I hope this works for you too!