Posting here as the main page links the forum for tech support.
Tabs across multiple windows pointing to the same file can get out-of-sync, and you can lose data even if you save frequently.
I wrote up some details and steps to produce the issue here:
https://github.com/SublimeTextIssues/Core/issues/2870
On a related note: For anyone else experiencing the same issue, do you have any suggestions for workarounds?