AppCast download randomly results in various NSURLErrorDomain codes

[psulak]

We have a non-Sandboxed app that’s currently linked against Sparkle v2.3.2.

Our app’s had a long-standing random issue where Sparkle is unable to download the AppCast from our Server. We routinely see SUSparkleErrorDomain code SUDownloadError with underlying NSURLErrorDomain codes like:

-1001 (timeout)
-1003 (can’t find Host)
-1005 (network connection was lost)
-1009 (not connected to Internet)
-1200 (secure connection failed)

Ironically the reason we know these failure codes is that we have our app immediately Log the error to our Server via a POST NSURLSessionDataTask (which works even after the NSURLErrorDomain failure from the AppCast). We get maybe 10-20 new logs each day with this issue, all from unique IP's, different versions of macOS, and both Intel and Apple Silicon hardware. There doesn’t seem to be any rhyme or reason to the problem.

We've never been able to reproduce the problem in-house. But several years ago I added a “Retry” system when downloading the AppCast. We think that alleviated some of the problem, but it’s never entirely gone away.

Do you guys have any suggestions on what may be happening? Again, we’re a non-Sandboxed app. One thought I had (after browsing various issues here on GitHub) was that our AppCast URL uses HTTPS. But I was thinking about switching the URL to HTTP on the final attempt in my Retry system. Do you think that might help?

Thanks in advance.