Open a task and tap History. Each change is listed in plain words, newest first, with when it happened and on which device: “Do date set to Friday”, “Estimate set to 45m”, “Completed”.
With iCloud sync, if two devices changed the same thing before they synced, the entry says Changed on two devices and shows which change was kept. Nothing disappears without a trace.
History is kept for a year, on every device you sync.
Checked against Billine 1.0