It works now, for me, and I’ve been using it a lot (see next paragraph). Wireshark used to look extremely messy, possibly to the point of causing the server to close, as shown on my trace above. I didn’t show the subsequent close packets, just the initiation from server side. After cable modem restart, my download benchmark is right where it should be on a random speed test (before, it was 20 Mbits/second or worse). Wireshark is showing occasional downstream packet loss (and TCP Dup Ack to recover), so looks normal. When connection was unreliable though, nothing else got to a total failure besides the Duplicati download from its update server, so something seems sensitive. A download from www.duplcati.com (S3) completed.
Agree on the first part, which is the workaround for this longstanding problem. For the second part, there’s accumulating evidence at Activate downloaded upgrade sometimes fail that it doesn’t work as it should work. Continuing the conversation there would probably be more productive, and will keep this thread uncluttered.