Can you see if this commit helps?
https://github.com/discourse/discourse/commit/ce4b5b56e5fbf53438592b865c733759ebfa95c3
We had a condition where drafts could be saving “concurrently” meaning the composer could be in the middle of saving a draft and another draft save would be issued. This only happened when network latency is high, but I think it is quite likely you were a victim to this @xiasummer
No guarantees that it fixes it, this is some very complex code, but on all my local testing it is working much better.