Junecloud Sync has a limit of around 65K per note. If your note is in English, the limit will be around 65,000 characters. In other languages, like Japanese, it will be closer to 25,000 characters.
The current version of the Notefile app does not deal with this situation well, and will not show an error. In the past you may have seen frequent “couldn’t connect” errors. This issue will be addressed in a future update.