Hello, all! I wanted to update this thread after doing a few hours of testing on my end. I was able to confirm that sync didn’t appear to work in some cases, but worked most of the time as I would expect. Allow me to elaborate.
To conduct my testing I setup Brave Nightly (v1.1.36.23) on my Windows 10 PC, and Brave (v1.32, 21.10.13.18) on my iPad. Both instances were removed from any existing sync chains beforehand.
I created a new sync chain from the iOS device, and manually entered the code words into my desktop device, thus connecting the two via a novel, common chain. Upon doing this, bookmarks were exchanged between devices. As @ukheather stated, everything appears to work when you first establish the new chain.
What Worked
I primarily tested bookmark-syncing, which I found to work flawlessly in my experience. In fact, not only did I run into 0 issues syncing bookmarks between devices, I was impressed with how quickly changes were propagated.
I created bookmarks from desktop, and saw them appear on iOS. I created bookmarks from iOS, and saw them appear on desktop. I deleted bookmarks on both ends, and saw them be removed almost immediately from the other device. I also did edits (changing a title, or moving from one folder to another) and saw those applied within seconds to the other device.
What Didn’t Work (or didn’t work well)
After confirming that bookmarks were working reliably for me, I enabled history-sync on both devices and began testing that scenario. I would type a URL into desktop, and wait for it to appear in Brave’s history on iOS. I would also type a URL into iOS, and wait for it to appear in Brave’s history on desktop. This scenario worked sometimes, but not always, and usually only in one direction (sending desktop URLs to iOS).
When I first enabled History Sync on iOS, recently-visited domains were synced to the desktop device. Viewing the updated history on desktop requires a manual refresh of the desktop history page, which is not the case for iOS.
As @ukheather described in earlier posts, there were indeed some issues after the initial sync. I couldn’t get many history items (i.e. typed URLs) to sync from iOS to desktop. Desktop to iOS worked very reliably, but mobile-history rarely appeared in the history of the desktop instance of Brave (out of half a dozen or so URLs tested, 1 or 2 sync’d to desktop).
It’s unclear at this time where the problem lies; it could be an issue with iOS failing to recognize the opportunity to sync history from time to time. I am already speaking with the iOS team about investigating their possibility further.
Other Notes
My testing involved proxying all iOS network activity through the desktop device where Brave Nightly was running. Traffic for both Brave Nightly on Windows, and Brave on iOS, passed through the Web Proxy Debugger Fiddler Classic (by Telerik).
Although I had trouble syncing history (again, bookmarks worked very reliably) from iOS to desktop, both browser instances remained in good communication with the Sync endpoint (sync-v2.brave.com at the time of this writing). I never noticed any interruptions in communication with the Sync server itself.
Conclusion
I’m convinced there is indeed an issue here which prevents, at the very least, history from being synced from iOS to desktop (or presumably any other device on the sync chain). I’m going to spend more time looking into this, and hope to have more updates to share in the near future.