This sounds like WAI, my understanding is that sync entities are not allowed to exceed something like 8KB each. It's a bit concerning that 1900 characters would result in >8 KB though, I'll try to investigate, time permitting.

Testing this, I can get a URLs significantly longer than 1,900 characters to sync, I definitely was able to get 9,000 character urls to work, and it would seen that 10,000 character urls failed. It seems my previously assumed max entity size of 8KB is slightly wrong, the actual limit is closer to 10KB. And fortunately we're not doing anything inefficient with encoding that's artificially lowering this threshold, nor are the limits applied after any sort of compression.

It seems that we claim SUCCESS on any over-sized entities, and silently fail to persist the changes. This would actually be really bad if you had a bookmark folder with a name >10000 characters long, although I have a difficult time imagining a use case for this, since that shouldn't be a URL.

It's also important to note that urls like chrome://blahblah and file:///blahblah will not sync, unless there are other more interesting/syncable navigation entries in that tab (within +/- 5).

So, back to your original problem, I'm hoping you miscounted the number of characters in your URL, or it was not syncable. Otherwise there's a different problem that's presenting here! Adding Needs-Feedback, perhaps you could try again and see if 1,900 character URLs are still causing problems? Do you think you could post a 1,900 character URL that doesn't work for you, so I could try it?

No response to questions in c#2.